COLORADO PLATEAU REGION 
CONSIDERED AS 
A FIELD FOR GEOLOGICAL STUDY, 
BY 
G. Iv . G I L B E R T , 
Washington, D. C. 
[From the American Journal of Science and Arts, July and August, 1876. | 
N E W HAVEN: 
TUTTLE, MOREHOUSE & TAYLOR, PRINTERS. 
1876. [From the American Journal of Science and Arts, July and August, 1876.] 
THE COLORADO PLATEAU PROVINCE AS A 
FIELD FOR GEOLOGICAL STUDY. 
I. Definition and Description of the Province. 
In the Mississippi Valley and “the Plains” the strata are 
almost undisturbed and lie nearly level. They have, indeed, 
been lifted above the parent ocean, and in part raised to a height 
of thousands of feet, but broad areas have moved together and 
all flexures have been gentle. There are no traces of the fold- 
ings which characterize the Appalachian region. The preva- 
lent features of topography are plains and hills. 
From the western edge of the plains to the Pacific Ocean 
the characteristic features are mountains. The strata are bent 
and broken, and upturned at all angles. The typical structures 
are structures of displacement. Within this region of great 
disturbance is a restricted area of comparative calm. Disloca- 
tions of strata are not unknown in it; indeed they are of fre- 
quent occurrence; but they are less frequent, less profound, 
and less complex, than in the surrounding region of mountains. 
Its mountains are few and scattered, and its typical topographic 
form is the table or plateau. It is called the Colorado Plateau 
Province. 
This region of plateaus was crossed by many lines of early 
exploration, and the salient features of its topography were 
described by numerous observers. The first writer who called 
attention to the extent of the district, and colligated the northern 
portions with the southern, was Professor W. P. Blake (Pac. 
R. R. Repts., vol. iii, part iv, pp. 8 and 42, 1856.) The title of 
“Colorado Plateau” first appeared in the map of Ives’ Colorado 
River Report in 1861, and was written between San Francisco 
Mountains and the Grand Canon. Later usage extended the 
term to include the broad upland through which the Colorado 
has excavated its deep channel; and finally, as the minor pla- 
teaus of which the great one is composed began, in the progress 
of geographical knowledge, to be discriminated and named, the 
comprehensive title of the whole became the Colorado Plateaus 
or the Colorado Plateau Province. Portions of the region have 
been studied, described, and mapped bv numerous geologists 
and geographers, but the chief contributions to our knowledge 
of the province as a whole, and of its limits, have come from the 
surveys conducted by Major Powell and Lieutenant Wheeler.* 
* Exploration of the Colorado River of the West and its tributaries; by J. W. 
Powell. Washington, 1875. 
U. S. Engineer Explorations and Surveys west of the 100th meridian, vol. iii, 
Geology; by G. K. Gilbert, Archibald R. Mar vine, Edwin E. Howell, and J. J. 
Stevenson. Washington, 1876. 2 
The Colorado Plateau Province. 
It would avail little to describe in detail the boundaries of the 
province without the aid of a map. On the east it is separated 
from the plains by a continuous broad belt of mountains, which 
include the parks of Colorado and have been called the Park 
Mountain System. On the south and west it adjoins the Basin 
Range Province, a region of many short parallel ranges, sepa- 
rated by trough-shaped, desert valleys. Northward it is limited 
by mountains for which there is no comprehensive title. Its 
greatest extent from north to south is 700 miles; from east to 
west, 425 miles. It comprises, of southern Wyoming, 20,000 
square miles; of eastern Utah, 50,000; of western Colorado, 
30,000; of northeastern Arizona, 45,000; and of northwestern 
New Mexico, 25,000;* making a total of 170,000 square miles, 
or one-twenty-fourth part of the territory of the United States. 
It is drained chiefly by the Colorado of the West and its tribu- 
taries, but the Sevier river heads in the western margin, and 
the Puerco of the East in its eastern, and the North Platte drains 
its northeastern angle. The plateaus which compose it range 
in altitude from 5,000 to 11,000 feet above the sea, but the 
lines of drainage are much lower, and the streams run at the 
bottoms of deep gorges or canons. The plateaus are terminated 
in part by cliffs, and the canon walls are cliffs. Plateaus, canons, 
and cliffs are the characteristic features. The chief mountains 
are of volcanic origin, and they are doubly conspicuous, since 
they not only constitute some of the loftiest points, but are 
exceptional to the general character of the topography. 
The climate is extremely dry—so dry that agriculture is 
impossible without irrigation. Vegetation is scant, except upon 
the heights. Below 8,000 feet altitude it is too sparse to inter- 
fere with the examinations of the geologist, aud there are vast 
stretches of absolutely naked rock. Travel is greatly obstructed, 
except along certain lines, by deep canons which ramify through 
the plateaus, and the selection of routes for wagon-roads and 
railroads is a work of great difficulty. 
All this description applies more especially to the southern 
portions of the district. North of the Uintah Mountains the 
streams flow in shallower and broader valleys, and are more 
sluggish. The Grreen river, the main artery of drainage, is there 
less deeply sunken in the plain than in its lower course, and all 
erosion by running water is hence less powerful. The profiles 
of the topography are more rounded, and accumulations of local 
drift and soil give rise to many grassy plains. 
The only important economic mineral of the whole region is 
* In defining the province in my report to Lieut. Wheeler (see U. S. Eng. Expl. 
and Sur. W. of the 100th mer., vol. iii, Geology, pp. 43 and 542) 1 have not included 
the portion south of the Uintah Mountains. I was not aware, at the time of writ- 
ing, that the plateaus south of the Uintas were continuous with those of Wyoming, 
the Uinta uplift not extending eastward to the Park Mountains. The Colorado Plateau Province. 
3 
coal, and this, though unlimited in quantity, is now utilized 
only where the Pacific railroad affords a market. Mines of the 
precious metals are nearly unknown, and in default of these, 
which are the usual incentives to settlement in our arid territo- 
ries, the region is chiefly uninhabited by the whites, and portions 
are even unexplored, except by the ubiquitous trapper and pro- 
spector, who make no record of their discoveries. Along the 
western margin are Mormon settlements. The market afforded 
by the Pacific railroad and its dependencies, has stimulated a 
little farming in Wyoming, and the same result has been wrought 
at the south, in Arizona and New Mexico, by a line of military 
posts. But in the center of the province one can find a spot 
that is more than one hundred miles from the nearest house, 
excepting only the ruined and abandoned dwellings of the 
Peublo Indians, who once peopled this forbidding land more 
densely than it is likely ever to be peopled again. 
II. How the material is exposed for study. 
As a field for the studies of the geologist, the Plateau Province 
offers valuable matter in an advantageous manner. Let us be- 
gin with the consideration of the manner. 
First, the Climate. The air is so dry that, except on the heights 
and at the margins of springs and streams, there is no turf no 
accumulation of humus, often no soil, and so little vegetation 
that the view is not obstructed. From a commanding emi- 
nence one may see spread before him, like a chart, to be read 
almost without effort, the structure of many miles of country, 
and in a brief space of time may reach conclusions, which, in a 
humid region, would reward only protracted and laborious ob- 
servation and patient generalization. There is no need to search 
for exposures where everything is exposed. Dr. Newberry, 
speaking of one of the southern plateaus, says, “ On our way 
to the Moqui villages we passed through a region singularly 
favorable for accurate geological investigation ; where there 
is no vegetation to impede the view; where the strata are 
entirely undisturbed, and are cut by valleys of erosion, in the 
wall-like sides of which every inch of the series may be exam- 
ined. In this journey we ascended in the geological scale from 
the summit of the Carboniferous to the base of the Cretaceous 
series. Of this interval there is no portion of which the expos- 
ures are not as complete as could be desired.” (Greol. Ives’ 
Exped., p. 77.) 
This aridity is not peculiar to the Plateaus: it pertains to the 
Basin Ranges, and in a less degree to the Plains. But in the 
Ranges the most arid portions are the valleys between the 
mountain ridges, and these are filled with monotonous Quater- 
nary gravels and clays, which hide all other beds, while the 
ranges themselves, which are of more interest to the geologist, 4 
The Colorado Plateau Province. 
catch all the precipitation, and are in some degree clothed with 
verdure. 
Second, the Drainage. The Plains and the Plateaus are alike 
drained by great rivers, which rise in lofty mountain regions, 
and traverse them on their way to the sea; but there the resem- 
blance ceases. The rivers which cross the Plains flow over 
them in broad shallow valleys. The soft rocks of the interven- 
ing benches decay more rapidly than they are undermined, and 
their rounded outlines are clothed with soil. But the Colorado 
and its branches flow across the Plateaus in deeply carved, nar- 
row canons. Where the Green river, which is the main fork 
of the Colorado, enters the Uintah Mountains, it is 2,000 feet 
below the adjoining plateau, and where the Colorado leaves the 
Plateaus, it emerges from a gorge 4,000 feet deep. In the inter- 
val the current courses, almost without exception, between high 
canon walls. Into this deep channel are gathered the waters 
of the uplands. Empowered bj* the rapidity of its descent, 
each tributary river has carved a canon of its own, and so too 
has each branch and creek tributary to a river, until the whole 
tract is divided by a labyrinth of ramifying canons. When the 
rain falls—for it does sometimes fall here—it flows down rapidly 
into the gorges, and washes with it the loosened particles of 
disintegrating rock. Then in time of flood the deepening wa- 
ters, constrained to a narrow channel, rush forward with impet- 
uous velocity and sweep out the detritus. The rocks of the 
upland are removed as fast as they decay, and soil cannot accu- 
mulate. Thus does thorough drainage conspire with aridity to 
prepare for the geologist a land of naked rock. 
No less important to the student are the canons themselves. 
They bear the same relation to a plain that geological cross- 
sections do to a geological map. They introduce in all cate- 
gories of observation a third dimension, and enable the con- 
templation of all the phenomena of structure with reference to 
depth as well as length and breadth. 
Third, Glacial drift and Lava-sheets. While these are, in them- 
selves, fertile subjects of study, they are also obstructions to 
observation, in so far as they conceal other formations from 
view ; and it is as obstructions that I here refer to them. 
Moraines are unknown in the southern half of the Plateau 
province, and in the northern they are not found at a lower 
altitude than 7,500 feet. The few that exist pertain to what 
were local glaciers. There was no general ice-mantle. The 
southern limit of glacial phenomena is in north latitude 38° 30', 
or about on the parallel of St. Louis. In the epoch of ice the 
climate of the Plateaus doubtless bore the same relation to that 
of the eastern seaboard that it does now. It was then, as now, 
a little colder than the latter, and a great deal drier; and it was 
its dryness which prevented, even at an altitude of some thou- The Colorado Plateau Province. 
5 
sands of feet, the accumulation of such a deluge of ice as visited 
the Atlantic seaboard in the same latitude. Only on the high- 
est mountains was the winter’s precipitation in excess of the 
summer’s melting. 
But while the mantling by glacial drift is inconsiderable, 
that by extravasated material is of great extent. Some of 
the largest continuous lava fields of our country belong to 
the Plateau region. A field in southern Utah stretches ninety 
miles from north to south and seventy miles from east to 
west; and the corresponding dimensions of one in New Mex- 
ico and Arizona are one hundred and seventy-five, and one 
hundred and forty miles. Almost coalescent with the latter is 
a third field which includes the San Francisco group of peaks 
in Arizona. Beneath these, and beneath minor floods of lava, 
are buried a tenth part of the sedimentary rocks of the Plateaus. 
In brief, the strata of the Plateau region are exposed with 
exceptional thoroughness. They are indebted to a dry climate, 
in ancient and modern times, for the almost entire absence of 
glacial drift, and for the suppression of vegetation. They are 
indebted to peculiar conditions of drainage for their poverty of 
soil, talus, and local drift, and for a system of natural cross- 
sections. Their chief detraction is a mere restriction of their 
area of exposure by overlapping lavas. 
III. The material for study. 
It remains to consider the nature of the material which is so 
fully exhibited, and examine its claims to attention. It pertains 
chiefly to four departments of geological investigation, viz : 
Mountain building by displacement; Mountain building by 
eruption ; Stratigraphy ; and Erosion ; and will be discussed 
under these heads, in the order indicated.* 
Mountain building by displacement. The Plateau Province 
differs from the mountain provinces by which it is surrounded 
in the degree and not in the kind of disturbance to which its 
sediments have been subject. Faults and folds abound through 
its whole extent, but they are comparatively of great simplicity. 
* The writer traveled, during three summers, with field parties of the Survey 
in charge of Lieut. George M. Wheeler of the U. S. Engineers, and during a fourth 
with a field party of the Survey in charge of Major J. W. Powell. His reports to 
Lieut. Wheeler are published in the third volume of the reports of “ Explorations 
and Surveys west of the 100th meridian.” Besides his own observations, the chief 
sources from which he has derived the material here presented, are: 1. The ob- 
servations of Major J. W. Powell, published in his report on the ‘‘Exploration of 
the Colorado River of the West and its tributaries;” and, in part, unpublished. 2 
and 3. The observations of Mr. E, E. Howell and of the late Mr. A. R. Marvine, 
published in vol. iii, of Lieut. Wheeler’s Reports, and in part unpublished. 4. The 
observations of Dr. J. S. Newberry, published in Ives’ ‘‘Explorations of the Colo- 
rado,” and in part unpublished. 5. The writings of Mr. Clarence King, “ Fortieth 
Parallel Survey,” vol. iii. 6. Mr. T. B. Comstock’s report in the U. S. Engineers’ 
“ Reconnaissance of northwestern Wyoming.” 7. Prof. E. D. Cope’s report to 
Lieut. Wheeler, published in the U. S. Engineer report for 1875. 6 
The Colorado Plateau Province. 
They are indeed so simple that they can be completely known. 
Their entire phenomena may be comprehended, measured, de- 
scribed, and delineated. The course of many a fault can be 
traced from end to end, and its-throw measured at every step. 
The form of many a fold can be determined throughout, and 
pictured or modelled in miniature, with every detail of flexure. 
Now, faults and folds are the elements of the displacements 
which give rise to mountains, and to study them is to study 
the very rudiments ot‘ mountain structure, and to acquire a 
knowledge of mountain structure is to lay the indispensable 
geological foundation for a true theory of the origin of moun- 
tains. Hence the value of this opportunity to study the elements 
of displacement in an uncombined condition, and in their sim- 
plest compound forms. To enforce this proposition, which is 
of more importance than might at first appear, I will take an 
illustration from the material already gathered, and, to do so, it 
will be necessary to explain one or two terms that have had to 
be coined to describe the new group of facts. 
In an anticlinal fold the 
strata dip in two directions 
away from the axis. In a 
synclinal fold the strata dip 
from two directions toward 
the axis. There is in nature 
a third type, which involves 
a dip in only one direction. 
This is the monoclincil fold. It is a double flexure, connecting 
strata at one level with the same strata at another level. In 
figure 1, the curvature between aa and bb is a monoclinal fold. 
It is evident that if two monoclinal folds are combined back 
to back, the result will be an anticlinal; if they are joined foot 
to foot, they will form a synclinal. Hence the monoclinal fold 
is a simpler element of displacement than either of the others. 
When a portion of the earth’s crust—it may be one that is 
measured by miles, or one that is measured only by feet—is 
moved bodily either up or down, while the portion adjacent to 
it is not so moved, the line along which they adjoin, will be 
marked by a fault, by a monoclinal fold, or by some combina- 
tion of the two. The fault and the monoclinal fold are alter- 
native manifestations of simple displacement, and are, in a cer- 
tain sense, equivalent. There are several different ways in 
which they are combined with each other. If one travels along 
the line of displacement that vseparates two blocks of strata 
which stand at different levels, he may find that at one point 
the beds are continuous, and curve downward from the upper 
level to the lower; and that at another point they are broken 
across, and the dissevered edges have slidden past each other. 
Fig. 1 The Colorado Plateau Province. 
7 
Or, if one could descend 
into the earth along the 
plane of dislocation, he 
might find that one stra- 
tum had been fractured, 
while another, less rigid, 
or coerced perhaps by a 
greater pressure of super- 
incumbent rock, had been only flexed. A third mode of com- 
bination is exhibited when a bed yields at first by flexure, and 
is finally fractured before the completion of the dislocation. 
These phenomena are illustrated by figure 2, which is an ideal 
representation of two blocks of strata, A and B, cut out from 
their surroundings, so as to exhibit the manner of their relative 
displacement. The front of the segment shows a flexed bed 
underlying a faulted one. The top of the segment shows a fault 
at the front, a monoclinal fold at the back, and a compound 
displacement midway. 
The monoclinal fold is not unknown in other parts of the 
world, but it has attracted little attention, and I am not aware 
that it has been described as abundant in any region. But in 
the region of the Plateaus it is not merely a feature of occasional 
occurrence; it is a characteristic type of displacement, and is 
rivalled in frequency only by the fault. 
Let us now turn from the displacements, to the disturbed 
masses of rock which they divide. A fault or a monoclinal 
fold is merely the record, at the margin of a solid block, of a 
movement that has affected the entire block, and it bears the 
same subsidiary relation to the movement of the block, that a 
line bears to the angle or area which it limits and defines. A 
large portion of the Plateau region is divided into great blocks 
—usually a few miles in width and many miles in length—and 
these have been unequally lifted above the ocean which de- 
posited their common sediments, so that each differs from its 
neighbor in altitude. They are bounded by lines of displace- 
ment. The blocks which have been lifted highest have been 
most exposed to erosive agencies, the tendency of which is to 
pare away eminences and reduce all to a common level: but as 
a rule, the highest plateaus mark the positions of blocks that 
have risen above their neighbors. The forms of many blocks 
are perfectly portrayed in the topography, and all can readily 
be traced out and defined by the study of the displacements. 
In illustration I have borrowed, through the kindness of 
Major Powell, a wood-cut from the report of his “ Exploration 
of the Colorado,” and if the reader will examine it attentively, 
he will obtain a clearer idea of the structure I have described, 
than I can hope to convey in words. The sketch is not an 
ideal one, but was carefully drawn to represent a tract of 
Fig. 2. 8 
The Colorado Plateau Province. 
Echo Cliff. 
Paria Displacement. 
Marble Canon Block. 
Paria Plateau, 
Marble Canon 
East Kaibab Displacement. 
Kaibab Block. 
Kaibab Plateau. 
West Kaibab Displacement. 
Kanab Creek. 
Kanab Block. 
Toroweap Displacement. 
Uinkaret Mts. 
Uinkaret Block. 
Pine Yalley Mts. 
Hurricane Displacement. 
Pig. 3. Section from west to east across the plateaus north of the Grand Canon 
of the Colorado, with bird’s-eye view above. Horizontal scale, 16 miles to the 
inch; vertical scale, 4 miles to the inch. The base line marks the level of the 
ocean; the dotted line above it the level of the river. The Colorado Plateau Province. 
9 
country, lying in Utah and Arizona, of which the main geolog- 
ical features are clearly understood. The geological section in 
the foreground is, in the main, the section which is exposed in 
the walls of the Grand Canon, and is 106 miles long. The 
vertical scale is four times as great as the horizontal. The base 
line marks the level of the ocean, and the dotted line the 
level of the Colorado river. The rock bed marked with small 
circles stands for the Lower Aubrey Group, a member of the 
Carboniferous System ; the one above it for the Upper Aubrey 
Group, also Carboniferous, and the dotted stratum, seen at the 
right, is the so-called Trias. In the bird’s-eye view beyond the 
section, the foreground is of plateaus floored by the limestone 
of the Upper Aubrey, and beyond rise terraces built, of Triassic 
and more recent strata. Five displacements are exhibited. 
Beginning at the left: the Hurricane displacement is a fault 
where it is intersected by the section, and has a throw of 2,500 
feet. Seventy miles farther north it is a combination of fault 
and fold. The throw of the To-ro'-weap fault is only 800 feet, 
and it disappears altogether in a few miles. The West Kai'-bab 
displacement is a monoclinal fold as far as it appears in the 
sketch, but farther south it changes to a fault. Its throw is 
2,000 feet. The East Kaibab displacement is a double mo- 
noclinal fold in the foreground but a single one in the distance. 
Its total throw is 3,000 feet. The throw of the Paria displace- 
ment is 1800 feet. It is known only as a simple fold. Along 
the lines of the first three displacements the eastern wall has 
risen, or the western has fallen ; but with the remaining two 
the reverse is the case. 
Between the Hurricane and Torroweap faults is contained the 
U'-in-ka-ret block. It is tilted slightly toward the east and is 
fifteen miles broad. Upon it stands a group of volcanic mount- 
ains, the lavas of which have risen through fissures in the 
block. Between the Toroweap and West Kaibab displacements 
is the Kan-ab' block, thirty miles broad. It appears level in 
the east-west section, but has, in common with all the other 
blocks of the sketch, a gentle dip to the north. Its cap of Car- 
boniferous limestone is divided in the foreground by the canon 
of Kanab creek, and fifty miles away it passes beneath Triassic 
sandstones. The Kaibab block stands highest of all. The 
strata, which for fifteen miles run level on its summit, are flexed 
downward at both margins, on one side to the Kanab block, 
and on the other to the Marble Canon block. Its upper sur- 
face is the Kaibab Plateau. The Marble Canon block is 
thirty miles broad. On the line of the section its highest 
bed is of Carboniferous age, but a few miles farther north it 
retains a heavy bed of Trias, which rises 2000 feet higher and 
constitutes the Paria Plateau. 
The features of the region pictured to which I wish, espe- 
cially to call attention, are : 10 
The Colorado Plateau Province. 
First, that there are no anticlinals and no synclinals, but 
only monoclinals and faults; 
Second, that the throws of the displacements are not all on 
the same side; 
Third, that the visible portion of the earth’s crust is divided 
into great blocks, which have changed their relative and absolute 
altitudes by thousands of feet, without losing their individuality. 
The structure of this region is an unusually pure example of 
a type that, with various modifications, prevails throughout 
the Plateau region, and Major Powell has taken a name from 
the locality and called it the Kaibab structure. We cannot 
study the embryology of mountains by observing the progress 
of an individual, but it is possible, by the comparison of many 
individuals in various stages of development, to learn some- 
thing of the manner of mountain growth, and, studying the 
subject in this way, the conclusion has been reached that many 
mountain ranges are built upon the plan of the Kaibab Plateau. 
The essential feature of the plan is the upward movement en 
masse of a great body of rock between two planes of displace- 
ment. A plateau is thus produced, from which mountain forms 
are carved by the ordinary processes of erosion. Evidences of 
such a plan have been found in nearly all the mountains of the 
upper basin of the Sevier River, in some of the ranges of the 
Great Basin, by Major Powell in the Uintah range, and by Mr. 
Marvine in the Front and Medicine Bow ranges of Colorado. 
Few of these cases are so simple as that of the Kaibab Pla- 
teau. In some the block has been lifted more on one side than 
on the other, so as to acquire a dip; in other cases there are a 
number of blocks of different elevation in the same range; in 
yet other, the blocks are somewhat curved. 
I shall not attempt to enumerate the variations of the type, 
which arise in these several ways. The purpose of the illustra- 
tion is accomplished, if I have shown that the exceptional 
exhibition, in the Plateaus, of displacements which are simple 
and easy of comprehension, has already led to the recognition 
of a new class of mountain structures, or at least of a class so 
little known heretofore that it has not found place in the man- 
uals of geology. 
When the displacements of the region have all been worked 
out, it will be possible to construct a model which shall exhibit 
the structure of at least one hundred and fifty thousand square 
miles of the earth’s crust, showing the form and position of 
each of the blocks which compose it; and I conceive that such 
a model, or an equivalent presentation of the same material by 
some other method, will not be inferior in value to any 
single contribution that has been made to our knowledge of 
the results of orographic movements. The Colorado Plateau Province. 
11 
Jfountain building by eruption.—The studies, which the Pla- 
teaus afford in the phenomena of eruption, are scarcely less 
interesting and important than those of uplift and downthrow ; 
but they have received less attention up to the present time. 
It happens that a number of extinct eruptive mountains stand 
near the canons of the Colorado River. The country about 
them has suffered and is suffering rapid denudation, and not 
only are their bases nearly free from detritus, but their flanks 
are so deeply scored, and their summits are so degraded, that 
their internal structure is exhibited. Those that are best 
known have been found to be composed chiefly of sedimentary 
strata, protected from denudation by the superior durability of 
the eruptive rocks with which they are associated. 
In the U'-in-ka-ret mountains Major Powell found a mass of 
undisturbed strata, which had been preserved from erosion by 
a mantle of lava, while the surrounding country was degraded 
more than a thousand feet. The eruptions were extended 
through a long period of time, and the successive outflows 
mantled the flanks of the surviving strata almost as thor- 
oughly as they did the summit, so as to give the appearance, 
at first glance, of a range made up entirely of volcanic matter. 
In the Henry Mountains the strata are not undisturbed, but 
have been lifted into a number of bubble-shaped domes, one 
for each individual mountain of the group. Each dome has 
been fractured at top, and divided by fissures radiating from 
the center toward the sides, and all the fissures have been filled 
by molten rock. Moreover the strata have in many places 
cleaved apart, and lava sheets have been interleaved with them. 
Doubtless the intrusion of these dikes and sheets was accom- 
panied by extrusion, but none of the extruded masses appear 
to have survived the subsequent erosion. The mountains as 
they stand are simply domes of curved strata, each traversed 
by a plexus of crystalline dikes. 
Similar in structure to the Henry Mountains are Navajo 
Mountain, Sierra la Sal, and Sierra Abajo. Mount San Fran- 
cisco, and perhaps Mount Taylor, are related to the Uinkarets. 
This enumeration includes but a small portion of the volcanic 
mountains of the district, and to the two types of structure 
mentioned, several others might be added. But the mountains 
of the Uinkaret and Henry types are most favorably situated 
for study, and at the same time diverge most widely in charac- 
ter from those with which geologists are already familiar. 
Stratigraphy.—In the stratigraphy of the Plateaus attention 
has thus far been confined to questions that are chiefly of 
local importance, but a thorough study of the phenomena 
which are accessible can hardly fail to throw light on the 12 
The Colorado Plateau Province. 
principles of sedimentation. In the region of canons a single 
bed can be followed, upon one continuous outcrop, for hun- 
dreds of miles, and every modification that it undergoes can 
be traced step by step. Moreover, by reason of the ramifica- 
tions of canons, it is frequently possible to trace a bed toward 
all points of the compass, so as to learn its changes, not merely 
along a simple line, but throughout an extended area. With 
such exposures, unconformity cannot escape detection, and the 
history of a system of sediments can be made out with a com- 
pleteness that surely cannot be excelled elsewhere. 
Part II. Erosion. 
It remains to indicate the scope of the material bearing upon 
the subject of erosion, and with that intent I will discuss cer- 
tain problems which the region has propounded. The first 
may be called 
The Problem of the Canons. 
The deep gorges which so facilitate the examination of the 
strata and of their displacements, are themselves of interest as 
monuments of erosion. To account for their existence and un- 
ravel their history is to review the laws of erosion with great 
wealth of illustration. Results so extreme can have been pro- 
duced only under conditions equally extreme; and natural 
laws are often best tested and exemplified by the consideration 
of their operation under exceptional circumstances. Already 
the problem of the canons has been attacked, and I cannot better 
demonstrate its radical value than bv presenting the present 
aspect of the case. For this purpose it is necessary to give a 
summary statement of the processes of erosion and of the con- 
ditions which determine its rate. The matter is so complex 
that this cannot be done briefly without the omission of the 
less important factors, and in undertaking it I shall take the 
liberty of either disregarding or slighting all considerations 
which have not an important bearing on the problem in ques- 
tion. 
In order to analyse sub-aerial erosion, we must consider 
it (A) as consisting of parts, and (B) as modified by condi- 
tions. 
A. All indurated rocks and most earths are bound together 
by a force of cohesion, which must be overcome before they can 
be divided and removed. The natural processes by which the 
division and removal are accomplished make up erosion. They 
are called disintegration and transportation. 
Transportation is chiefly peformed by running water. The Colorado Plateau Province. 
13 
Disintegration is naturally divided into two parts. So much 
of it as is accomplished by running water is called corrasion, 
and that which is not, is called weathering. 
Stated in their natural order, the three general divisions of 
the process of erosion, are(l) weathering, (2) transportation, and 
(8) corrasion. The rocks of the general surface of the land are dis- 
integrated by weathering. The material thus loosened is trans- 
ported by streams to the ocean or other receptacle. In transit 
it helps to corrade from the channels of the streams other ma- 
terial, which joins with it to be transported to the same goal. 
(1.) In weathering the chief agents of disintegration are solu- 
tion, change of temperature, the beating of rain, and vegetation. 
The great solvent of rocks is water, but it receives aid from 
some other substances, of which it becomes the vehicle. These 
substances are chiefly products of the formation and decompo- 
sition of vegetable tissues. Some rocks are disintegrated by 
their complete solution, but the great majority are divided into 
grains by the solution of a portion ; and fragmental rocks usu- 
ally lose by solution the cement merely, and are thus reduced 
to their original, incoherent condition. 
The most rigid rocks are cracked by sudden changes of tem- 
perature ; and the crevices thus begun, are opened by the freez- 
ing of the water within them. The coherence of the more 
porous rocks is impaired and often destroyed by the same ex- 
pansive force of freezing water. 
The beating of the rain overcomes the feeble coherence of 
earths, and assists solution and frost by detaching the particles 
which they have partially loosened. 
Plants often pry apart rocks by the growth of’ their roots, but 
their chief aid to erosion is by increasing the solvent power of 
percolating water. 
(2.) A portion of the water of rains flows over the surface 
and is quickly gathered into streams. A second portion is ab- 
sorbed by the earth or rock on which it falls, and after a slow 
underground circulation reissues in springs. Both transport 
the products of weathering, the latter carrying dissolved min- 
erals, and the former chiefly undissolved. 
Transportation is also performed by currents of air, and by 
the direct action of gravity; but in the present discussion it 
will not be necessary to consider these accessory agents. 
(3.) In corrasion the agents of disintegration are solution 
and mechanical wear. Wherever the two are combined, the 
superior efficiency of the latter is evident; and in all fields of 
rapid corrasion the part played by solution is so small that it 
may be disregarded. 
The mechanical wear of streams is performed by the aid of 
hard mineral fragments which are carried along by the current. 14 
The Colorado Plateau Province. 
The effective force is that of the current; the tools are mud, 
sand, and bowlders. The most important of them is sand ; it is 
chiefly by the impact and friction of grains of sand that the 
rocky beds of streams are disintegrated. 
Streams of clear water corrade their beds by solution. Muddy 
streams act partly by solution, but chiefly by attrition. 
Streams transport the combined products of corrasion and 
weathering. A part of the debris is carried in solution, and a 
part mechanically. The finest of the undissolved detritus is held 
in suspension ; the coarsest is rolled along the bottom ; and there 
is a gradation between the two modes. There is a constant 
comminution of all the material as it moves, and the work of 
transportation is thereby accelerated. Bowlders and pebbles, 
while they wear the stream-bed by pounding and rubbing, are 
worn still more rapidly themselves. Sand grains are worn and 
broken by the continued jostling, and their fragments join the 
suspended mud. Finally the detritus is all more or less dis- 
solved by the water, the finest the most rapidly. 
In brief, (1) weathering is performed by solution; by change 
of temperature, including frost; by rain beating; and by vege- 
tation. 
(2) Transportation is performed chiefly by running water. 
(8) Corrasion is performed by solution, and by mechanical 
wear. 
Corrasion is distinguished from weathering chiefly by in- 
cluding mechanical wear among its agencies, and the import- 
ance of the distinction will be apparent when we come to con- 
sider how greatly and peculiarly this agency is affected by 
modifying conditions. 
In the region of canons, the progress of corrasion has out- 
stripped that of weathering, and to discover what conditions 
have determined this result, is to solve the problem of the 
canons. 
B. The chief conditions which affect the rapidity of erosion 
are (1) declivity, (2) character of rock, and (3) climate. 
(1.) In general, erosion is most rapid where the slope is steepest; 
but weathering, transportation and corrasion are affected in 
different ways and in different degrees. 
With increase of slope goes increase in the velocity of run- 
ning water, and with that goes increase in its power to transport 
undissolved detritus. 
The ability of a stream to corrade by solution is not notably 
enhanced by great velocity; but its ability to corrade by 
mechanical wear keeps pace with its ability to transport, or 
may even increase more rapidly. For not only does the bot- The Colorado Plateau Province. 
15 
tom receive more blows in proportion as the quantity of tran- 
sient detritus increases, but the blows acquire greater force from 
the accelerated current, and from the greater size of the mov- 
ing fragments. It is necessary, however, to distinguish the 
ability to corrade from the rate of corrasion, which will be seen 
further on to depend largely on other conditions. 
Weathering is not directly influenced by slope, but it is 
reached indirectly through transportation. Solution and frost, 
the chief agents of rock decay, are both retarded b}7- the excessive 
accumulation of disintegrated rock. Frost action ceases alto- 
gether at a few feet below the surface, and solution gradually 
decreases as the zone of its activity descends and the circulation 
on which it depends becomes more sluggish. Hence the rapid 
removal of the products of weathering stimulates its action, and 
especially that portion of its action which depends upon frost. 
If, however, the power of transportation is so great as to remove 
completely the products of weathering, the work of disintegra- 
tion is thereby checked ; for the soil, which weathering tends to 
accumulate, is a reservoir to catch rain as it reaches the earth, 
and store it up for the work of solution and frost, instead of 
letting it run off at once unused. 
In brief, a steep declivity favors transportation and thereby 
favors corrasion. The rapid, but partial, transportation of 
weathered rock accelerates weathering; but the complete re- 
moval of its products retards weathering. 
(2.) Other things being equal, erosion is most rapid when the 
eroded rock offers least resistance; but the rocks which are most 
favorable to one portion of the process of erosion, do not neces- 
sarily stand in the same relation to the others. Disintegration 
by solution depends in large part on the solubility of the 
rocks, but it proceeds most rapidly with those fragmental rocks 
of which the cement is soluble, and of which the texture is 
open. Disintegration by frost is most rapid in rocks which ab- 
sorb a large percentage of water and are feebly coherent. Dis- 
integration by mechanical wear is most rapid in soft rocks. 
Transportation is most favored by those rocks which yield by 
disintegration the most finely comminuted debris 
(3.) The influence of climate upon erosion is less easy to 
formulate. The direct influences of temperature and rainfall 
are comparatively simple, but their indirect influence, through 
vegetation, is complex, and is in part opposed to the direct in- 
fluence of rainfall. 
Temperature affects erosion chiefly by its changes. Where 
the range of temperature includes the freezing point of water, 
frost contributes its powerful aid to weathering ; and it is only 
where changes are great and sudden that rocks are cracked by 
their unequal expansion or contraction. 16 
The Colorado Plateau Province. 
All the processes of erosion are affected directly by the 
amount of rainfall, and by its distribution through the year. 
All are accelerated by its increase and retarded by its diminu- 
tion. When it is concentrated in one part of the year at the 
expense of the remainder, transportation and corrasion are ac- 
celerated, and weathering is retarded. 
Weathering is favored by abundance of moisture. Frost ac- 
complishes most when the rocks are saturated ; and solution, 
when there is the freest subterranean circulation. But when 
the annual rainfall is concentrated into a limited season, a larger 
share of the water fails to penetrate, and the gain from tempo- 
rary flooding does not compensate for the checking of all solu- 
tion by a long dry season. 
Transportation is favored by increasing water supply as 
greatly as by increasing declivity. When the volume of a 
stream increases, it becomes at the same time more rapid, and 
its transporting capacity gains by the increment to velocity as 
well as by the increment to volume. Hence the increase in 
power of transportation is more than proportional to the in- 
crease of volume. 
It is due to this fact chiefly, that the transportation of a 
stream which is subject to floods is greater than it would be if 
its total water supply were evenly distributed in time. 
The indirect influence of rainfall and temperature, by means 
of vegetation, has different laws. Vegetation is intimately re- 
lated to water supply. There is little or none where the annual 
precipitation is small, and it is profuse where the latter is great 
and especially where the temperature is at the same time high, 
In proportion as vegetation is profuse the solvent power of per- 
colating water is increased, and, on the other hand, the ground 
is sheltered from the mechanical action of rains and rills. The re- 
moval of disintegrated rock is greatly impeded by the conserv- 
ative power of roots and fallen leaves, and a soil is invariably 
preserved. Transportation is retarded. Weathering by solu- 
tion is accelerated up to a certain point, but in the end it suf- 
fers by the clogging of transportation. The work of frost is 
nearly stopped as soon as the depth of soil exceeds the limit of 
frost action. The force of rain-drops is expended on foliage. 
Moreover a deep soil acts as a distributing reservoir for the 
water of rains, and tends to equalize the flow of streams. 
Hence the general effect of vegetation is to retard erosion ; 
and since the direct effect of great rainfall is the acceleration 
of erosion, it results that its direct and indirect tendencies are 
in opposite directions. 
In arid regions of which the declivities are sufficient to give 
thorough drainage, the absence of vegetation is accompanied by The Colorado Plateau Province. 
17 
absence of soil. When a shower falls, nearly all the water runs 
off from the bare rock, and the little that is absorbed is rapidly 
reduced by evaporation. Solution becomes a slow process for 
lack of a continuous supply of water, and frost accomplishes 
its work only when it closely follows the infrequent rain. 
Thus weathering is retarded, and transportation has its work so 
concentrated by the quick gathering of showers into floods, as 
to compensate, in part at least, for the smallness of the total 
rainfall from which they derive their power. 
Hence in regions of small rainfall, surface degradation is 
usually limited by the slow rate of disintegration ; while in re- 
gions of great rainfall it is limited by the rate of transporta- 
tion. There is probably an intermediate condition, with mod- 
erate rainfall, in which a rate of disintegration greater than that 
of an arid climate is balanced by a more rapid transportation 
than consists with a very moist climate, and in which the rate 
of degradation attains its maximum. 
Having examined the conditions of erosion separately, let us 
now group them in such combination as will help to an under- 
standing of the canons. 
Over nearly the whole of the earth’s surface there is a soil, 
and wherever this exists we know that the conditions are more 
favorable to weathering than to transportation. Hence it is 
true in general that the conditions which limit transportation 
are those which limit the general degradation of the surface. 
To understand the manner in which this limit is reached, it 
is necessary to look at the process bv which the work is accom- 
plished. 
Transportation and Comminution. — A stream of water flowing 
down its bed expends an amount of energy that is measured by 
the quantity of water and the vertical distance through which 
it descends. If there were no friction of the water upon its 
channel the velocity of the current would continually increase; 
but if, as is the usual case, there is no increase of velocity, then 
the whole of the energy is consumed in friction. The friction 
produces inequalities in the motion of the water, and especially 
induces subsidiary currents more or less oblique to the general 
onward movement. Some of these subsidiary currents have an 
upwrnrd tendency, and by them is performed the chief work of 
transportation. They lift small particles from the bottom and 
hold them in suspension while they move forward with the 
general current. The finest particles sink most slowly and are 
carried farthest before they fall. Larger ones are barely lifted, 
and are dropped at once. Still larger are only half lifted; that 
is, they are lifted on the side of the current and rolled over, 18 
The Colorado Plateau Province. 
without quitting the bottom. And finally there is a limit to 
the power of every current, and the largest fragments of its 
bed are not moved at all. 
There is a definite relation between the velocity of a curreut 
and the size of the largest bowlder it will roll. It has been 
shown by Hopkins that the weight of the bowlder is propor- 
tioned to the sixth power of the velocity. It is easily shown 
also that the weight of a suspended particle is proportioned to 
the sixth power of the velocity of the upward current that will 
prevent its sinking. But it mast not be inferred that the total 
load of detritus that a stream will transport bears any such re- 
lation to the rapidity of its current. The true inference is, that 
the velocity determines the limit in coarseness of the detritus 
that a stream can move by rolling, or can hold in suspension. 
Every particle which a stream lifts and sustains is a draft 
upon its energy, and the measure of the draft is the weight 
(weighed in water) of the particle, multiplied by the distance it 
would sink in still water in the time during which it is sus- 
pended. If, for the sake of simplicity, we suppose the whole 
load of a stream to be of uniform particles, then the measure of 
the energy consumed in their transportation, is their total 
weight multiplied by the distance one of them would sink in 
the time occupied in their transportation. Since fine particles 
sink more slowly than coarse, the same consumption of energy 
will convey a greater load of fine than of coarse. 
Again, the energy of a clear stream is entirely consumed in 
friction on its bottom ; and the friction bears a direct relation 
to its velocity. But if detritus be added to the water, then a 
portion of its energy is diverted to the transportation of the 
load; and this is done at the expense of the friction upon 
the bottom, and hence at the expense of velocity. As the 
energy expended in transportation increases, the velocity 
diminishes. If the detritus be composed of uniform particles, 
then we may also say that as the load increases, the velocity 
diminishes. But the diminishing velocity will finally reach a 
point at which it can barely transport particles of the given 
size, and when this point is attained, the stream has its maxi- 
mum load of detritus of the given size. But fine detritus re- 
quires less velocity for its transportation than coarse, and will 
not so soon reduce the current to the limit of its efficiency. A 
greater per cent of the total energy of the stream can hence be 
employed by fine detritus than by coarse. 
Thus the capacity of a stream for transportation is enhanced 
by comminution in two ways. Fine detritus, on the one hand, 
consumes less energy for the transportation of the same weight, 
and on the other, it can utilize a greater portion of the stream’s 
energy. The Colorado Plateau Province. 
19 
It follows, as a corollary, that the velocity of a fully loaded 
stream depends (ceteris paribus) on the comminution of the ma- 
terial of the load. When a stream has its maximum load of 
fine detritus, its velocity will be less than when carrying its 
maximum load of coarse detritus; and the greater load corre- 
sponds to the less velocity. 
It follows also thata stream which is supplied with heterogene- 
ous debris will select the finest. If the finest is sufficient in quan- 
tity, the current will be so checked by it, that the coarser cannot 
be moved. If the finest is not sufficient, the next grade will 
be taken, and so on. 
Transportation and Declivity.—To consider now the relation 
of declivity to transportation we will assume all other conditions 
to be constant. Let us suppose that two streams have the same 
length, the same quantity of water, flow over beds of the same 
character, and are supplied to their full capacities with detritus 
of the same kind ; but differ in the total amount of fall. Their 
declivities, or rates of fall, are proportional to their falls. Since 
the energy of a stream is measured by the product of its vol- 
ume and its fall, the relative energies of the two streams are 
proportional to their falls, and hence, proportional to their de- 
clivities. The velocities of the two streams, depending as we 
have seen above, on the character of the detritus which loads 
them, are the same ; and hence the same amount of energy is 
consumed by each in friction on its bed. And since the energy 
which each stream expends in transportation is the residual 
after deducting what it spends in friction from its total energy, 
it is evident that the stream with the greater declivity will not 
merely have the greater energy, but will expend a less per cent 
of it in friction and a greater per cent in transportation. 
Hence declivity favors transportation in a degree that is 
greater than its simple ratio. 
[There are two elements of which no account is taken in the 
preceding discussion, but which need to be mentioned to pre- 
vent misapprehension, although they detract in no way from 
the conclusions. 
The first is the addition which the transported detritus makes 
to the energy of the stream. A stream of water charged with 
detritus is at once a compound and an unstable fluid. It has 
been treated merely as an unstable fluid requiring a constant 
expenditure of energy to maintain its constitution ; but looking 
at it as a compound fluid, it is plain that the energy it devel- 
opes by its descent, is greater than the energy pertaining to the 
water alone, in the precise ratio of the mass of the mixture to 
the mass of the simple water. 20 
The Colorado Plateau Province. 
The second element is the addition which the detritus makes 
to the friction of the stream. The coefficient of friction of the 
compound stream upon its bottom will always be greater than 
that of the simple stream of water, and hence for the same 
velocity a greater amount of energy will be consumed. 
It may be noted in passing, that the energy which is con- 
sumed in the friction of the detritus on the stream bed, accom- 
plishes as part of its work the mechanical corrasion of the bed.] 
Transportation and quantity of water.—The friction of a stream 
upon its bed depends on the character of the bed, on the area 
of the surface of contact, and on the velocity of the current. 
When the other elements are constant, the friction varies 
directly with the area of contact. The area of contact depends 
on the length and form of the channel, and on the quantity of 
water. For streams of the same length, and same form of cross- 
section, but differing in size of cross-section, the area of con- 
tact varies directly as the square root of the quantity of water. 
Hence, ceteris paribus, the friction of a stream on its bed, is pro- 
portioned to the square root of the quantity of water. But, as 
stated above, the total energy of a stream is proportioned direct- 
ly to the quantity of water. And also, the total energy is 
equal to the energy spent in friction, plus the energy spent in 
transportation. Whence it follows, that if a stream change its 
quantity of water without changing its velocity or other acci- 
dents. the total energy will change at the same rate as the quan- 
tity of water, the energy spent in friction will change at a less 
rate, and the energy remaining for transportation will change at 
a greater rate. 
It follows, as a corrollary, that the running water which car- 
ries the debris of a district, loses power by subdivision toward 
its sources ; and that, unless there is a compensating increment 
of declivity, the tributaries of a river will fail to supply it with 
the full load which it is competent to carry. 
It is noteworthy also, that the obstruction which vegetation 
opposes to transportation, is especially effective in that it is ap- 
plied at the infinitesimal sources of streams, where the force of 
the running water is least. 
A stream which can transport debris of a given size, may be 
said to be competent to such debris. Since the maximum parti- 
cles ’which streams are able to move are proportioned to the 
sixth powers of their velocities, competence depends on veloc- 
ity. Velocity, in turn, depends on declivity and volume, and 
(inversely) on load. 
In brief, the capacity of a stream for transportation is greater 
for fine debris than for coarse. The Colorado Plateau Province. 
21 
Its capacity for the transportation of a given kind of debris 
is enlarged in more than simple ratio by increase of declivity ; 
and it is enlarged in more than simple ratio by increase of vol- 
ume. 
The competence of a stream for the transport of debris of a 
given fineness, is limited by a correspondent velocity. 
The rate of transportation of debris of a given fineness, may 
equal the capacity of the transporting stream, or it may be less. 
When it is less, it is always from the insufficiency of supply. 
The supply which is furnished by weathering is never availa- 
ble unless the degree of fineness of the debris brings it within 
the competence of the stream at the point of supply. 
The chief point of supply is at the very head of the flowing 
water. The rain which falls on material that has been disin- 
tegrated by weathering, begins, after it has saturated the imme- 
diate surface, to flow off. But it forms a very thin sheet; its 
friction is great; its velocity is small; and it is competent to 
pick up only particles of exceeding fineness. If the material is 
heterogeneous, it discriminates and leaves the coarser particles. 
As the sheet moves on, it becomes deeper, and soon begins to 
gather itself into rills. As the deepening and concentration of 
water progresses, either its capacity increases and the load of fine 
particles is augmented, or, if fine particles are not in sufficient 
force, its competence increases, and larger ones are lifted. In 
either case the load is augmented, and, as rill joins with rill, it 
steadily grows, until the accumulated water finally passes be- 
yond the zone of disintegrated material. 
The particles which the feeble initial currents are not compe- 
tent to move, have to wait either until they are subdivided by 
the agencies of weathering, or until the deepening of the chan- 
nels of the rills so far increases the declivities, that the currents 
acquire the requisite velocity, or until some fiercer storm floods 
the ground with a deeper sheet of water. 
Thus rate of transportation, as well as capacity for transpor- 
tation, is favored by fineness of debris, by declivity, and by 
quantity of water. It is opposed chiefly by vegetation, which 
holds together that which is loosened by weathering, and shields 
it from the agent of transportation in the very place where that 
agent is weakest. 
When the current of a stream gradually diminishes in its 
course—as, for example, in approaching the ocean—the capac- 
ity for transportation also diminishes; and so soon as the 
capacity becomes less than the load, precipitation begins,—the 
coarser particles being deposited first. 
Corrasion.—If a stream has no load of detritus, it corrades 
only by solution. If it is loaded to its full capacity, it does 22 
The Colorado Plateau Province. 
notcorrade; it is on the verge between corrasion and deposi- 
tion. Only with a partial load does a stream wear its bottom. 
The rapidity of mechanical corrasion depends on the hardness, 
size, and number of transient fragments, on the hardness of the 
rock-bed, and on the velocity of the stream. The blows which 
the moving fragments deal upon the stream-bed are hard, in 
proportion as the fragments are large and the current is swift. 
They are most effective when the fragments are hard and the 
bed-rock is soft. Their number is increased, up to a certain 
limit, by the increase of the load of the stream ; but when the 
fragments become greatly crowded at the bottom of a stream, 
their force is partially spent among themselves, and the bed- 
rock is in the same degree protected. For this reason, and be- 
cause increase of load causes retardation of current, it is prob- 
able that the maximum work of corrasion is performed w7hen 
the load is far within the transporting capacity. 
The element of velocity is of double importance, since it de- 
termines, not only the speed, but, to a great extent, the size of 
the pestles which grind the rocks. The coefficients upon which 
it in turn depends, namely, declivity and quantity of water, 
have the same importance in corrasion that they have in trans- 
portation. 
Let us now direct our attention to the region of the canons. 
The Plateau province lay beneath the ocean up to the close 
of the Mesozoic age. In early Genozoic time it was nearly 
covered bv fresh-water lakes, and was not greatly elevated. 
In more recent epochs it has been very greatly, but unequally 
lifted, and the lakes have been drained. The erosion which 
began with the first lifting of a part above the ocean, and ex- 
tended its area as the lakes disappeared, has progressed contin- 
ually to the present time. The average total uplift has been about 
12,000 feet; the mean altitude of the present surface is about 
7,000 feet; and the difference is the mean amount of degrada- 
tion. While 5,000 feet have been removed from the general 
surface, an amount greater by several thousand feet has been 
corraded by the rivers. 
The greater tributaries of the Colorado have their sources 
in elevated mountains which are well supplied with rain. Their 
courses through the Plateaus traverse regions characterized by 
aridity. 
On the uplands which border the canons the supply of water 
is so small and the declivity is so great that weathering is less 
favored than transportation. No soil accumulates ; vegetation 
is scant; and, for the lack of these, weathering is reduced to a 
minimum. The degradation of the surface is limited by the 
retarded weathering. rThe Colorado Plateau Province. 
23 
In the canons corrasion is favored by a quantity of water which 
belongs to the mountain sources of the streams and not to the 
plateaus which they divide. It is favored by a great declivity 
of bed, for which it is indebted to the magnitude and recency 
of the uplift. It is favored by a moderate supply of debris, 
always sufficient for the work of excavation, but not so great 
as to consume the entire energy of the current. 
The contrast between the degradation of the upland and the 
cutting of the water ways is strongest where the rocks are best 
fitted to resist disintegration. The rivers sink their channels 
into the land in a harmonious and interdependent system, and 
cannot excavate soft beds more deeply than hard. But the 
only downward limit to the degradation of the tables is the 
level of the draining river system ; and the varying retardation 
which it suffers from the resistance of different rocks, is ex- 
pressed in the varying height of the canon walls. 
A second problem which has arisen in the study of the ero 
sion of the Plateaus may be called 
Where rivers descend aslope that is terraced by the alterna- 
tion of hard and soft strata, they are apt to leap from the edges 
of the hard beds in waterfalls. But the Colorado, notwith- 
standing the structure of its bed presents the most favorable 
conditions, makes no leap. At the head of Marble Canon, for 
instance, the river crosses a great bed of limestone, lying nearly 
level and underlaid by a great bed of friable sandstone. The 
limestone resists all erosive agents as strongly as does the Niag- 
ara limestone, and the sandstone yields to them as easily as 
does the Niagara shale. But, instead of plunging from one to 
the other in a great cataract, the Colorado cuts the tw<*> with 
nearly equal grade of channel. Its average descent in the hard 
rock is ten feet to the mile, and in the soft, less than five feet. 
It is evident that for the production of waterfalls some con- 
dition is involved beside that of the constitution of the rock- 
system which the stream traverses,—some condition that per- 
tains to the constitution of the stream itself. Such a condition 
is to be found in the relation of corrasion to transportation. 
Let us suppose that a stream, endowed with a constant sup- 
ply of water, is at some point continuously supplied with as 
great a load as it is capable of carrying. For so great a dis- 
tance as its velocity remains the same, it will neither corrade 
nor deposit, but will leave the grade of its bed unchanged. But 
if in its progress it reaches a place where a less declivity of bed 
gives a diminished velocity, its capacity for transportation will 
become less than the load, and part of the load will be depos- 
The Problem of "Waterfalls. 24 
The Cobrado Plateau Province. 
ited. Or if in its progress it reaches a place where a greater 
declivity of bed gives an increased velocity, the capacity for 
transportation will become greater than the load, and there will 
be corrasion of the bed. In this way a stream, which has a 
supply of debris equal to its capacity, tends to build up the 
gentler slopes of its bed and cut away the steeper. It tends to 
establish a single, uniform grade. 
Let us now suppose that the stream, after having obliterated 
all the inequalities of the grade of its bed, loses nearly the 
whole of its load. Its velocity is at once accelerated and corra- 
sion begins through its whole length. Since the stream has 
the same declivity, and consequently the same velocity, at all 
points, its capacity for corrasion is everywhere the same. Its 
rate of corrasion, however, will depend on the character of its 
bed. Where the rock is hard, corrasion will be less rapid than 
where it is soft, and there will result inequalities of grade. But 
so soon as there is inequality of grade, there is inequality of 
velocity, and inequality of capacity for corrasion ; and where 
hard rocks have produced declivities, there the capacity for 
corrasion will be increased. The differentiation will proceed 
until the capacity for corrasion is everywhere proportioned to 
the resistance, and no farther,—that is, until there is an equilib- 
rium of action. 
In general, we may say that a stream tends to equalize its 
work in all parts of its course. Its power inheres in its fall, 
and each foot of fall has the same power. When its work is to 
corrade and the resistance is unequal, it concentrates its energy 
where the resistance is great, by crowding many feet of descent 
into a small space; and diffuses it, where the resistance is 
small, by using but a small fall in a long distance. When its 
•work is to transport, the resistance is constant, and the fall is 
evenly distributed by a uniform grade. When its work in- 
cludes both transportation and corrasion, as is the usual case, 
its grades are somewhat unequal; and the inequality is greatest 
when the load is least. 
The condition of the Colorado in respect to load, is midway 
between that of the Niagara and that of the Platte. • 
The water of the Niagara is nearly devoid of load. The lake of 
which it is the outlet gathers the detritus of all tributary 
streams, and only on the occasion of a great storm yields a 
small portion of it to the Niagara. The work of transportation 
is at a minimum, and the differentiation of slope dependent on 
rock structure reaches its maximum in a cataract. 
The water of the Platte is supplied with all the load it can 
move. Major Powell, who has made a careful study of this 
river, ascribes its peculiar character to the fact that it flows 
through a region of unconsolidated strata. Its mean declivity The Colorado Plateau Province. 
25 
is as great as that of the Colorado, and it would have carved 
canons of imposing depth, if only the material of its banks were 
sufficiently coherent to stand in walls. As it is, the loose sands 
of the bordering plains are washed and blown into the river, 
and, its energy being consumed in their transportation, the cor- 
rasion of its channel can proceed no faster than the general 
degradation of the plain. Having little work to perform be- 
side the transportation of its load, it maintains an almost un- 
varied slope from the foot of the mountains to its mouth. 
In that portion of the Colorado which is contained in the 
Plateau province, the load consumes a share of the energy of 
the stream and leaves to corrasion the remainder. The slopes 
of the stream-bed are varied, but not so greatly as those of the 
Niagara. Where the bed-rock is soft, the declivity is small. 
Where it is hard, the declivity is relatively great; but in the 
toughest hornblende rock the mean angle of slope does not ex- 
ceed three degrees. 
The Problem of Inconsequent Drainage. 
There is a third problem of erosion now under investigation 
in the Plateaus that promises results of value and novelty. It 
was propounded by Major Powell, and is set forth on page 162, 
et seq., of his “Exploration of the Colorado Kiver.” The ques- 
tion to be answered is: What is the relation of the drainage 
system of the Plateaus to the system of displacements? How 
far is it consequent, how far antecedent, how far super-imposed ? 
If a series of sediments, accumulated in an ocean of lake, be 
subjected to a system of displacements while still under water, 
and then be converted to dry land by elevation en masse, or by 
the retirement of the water, the rains which fall on it will in- 
augurate a drainage system perfectly conformable with the 
system of displacements. Streams will rise along the crest of 
each anticlinal, will flow from it in the direction of the steepest 
dip, will unite in the synclinals, and will follow them length- 
wise. The axis of each synclinal will be marked by a water- 
course ; the axis of each anticlinal by a watershed. Such a 
system is said to be consequent on the structure. 
If, however, a system of displacements affect a rock series 
after the series has become continental, it will have already ac- 
quired a system of waterways, and, unless the displacements 
are produced with unusual rapidity, the waters will not be 
diverted from their accustomed ways. The effect of local ele- 
vation will be to stimulate local corrasion, and each river that 
crosses an uplifted block will, inch by inch as the block rises, 
deepen its channel and valorously maintain its original course. 
It will result that the directions of the drainage lines will be 26 
The Colorado Plateau Province. 
independent of the displacements. Such a drainage system is 
said to be antecedent to the structure. 
There is one other case. Suppose a rock series that has been 
folded and eroded, to be again submerged, and to receive a new 
accumulation of unconforming sediments. Suppose further, 
that it once more emerges, and that the new sediments are 
eroded from its surface. Then the drainage system will have 
been given by the form of the upper surface of the superior 
strata, but will be independent of the structure of the inferior 
series into which it will descend vertically as the erosion pro- 
gresses. Such a drainage system is said to be super-imposed 
uppn the structure of the older series of strata. 
A large share of the drainage of the Plateaus is not conse- 
quent. How much is super-imposed, and how much ante- 
cedent remains to be determined. With the solution of the 
problem are involved the determination of the antiquity and 
history of the Green and Colorado Rivers, and the physical 
history of the great Tertiary lakes; and we may hope that from 
its discussion will result the establishment of laws, by the aid 
of which it shall be possible, in other regions, to deduce facts of 
geological history from an examination of the relation of struc- 
ture to drainage. 
Summary. 
The exposure of the rock structure in the Colorado Plateau 
province is exceptionally thorough. Soil and vegetation ob- 
struct the view less than in other lands, and deep canons exhibit 
natural sections in many directions. 
The rock structure is simple but not the simplest. The 
strata have been displaced, but their displacement is so little 
complex that it can be clearly determined in kind and amount. 
In virtue of the simplicity of structure and continuity of ex- 
posure, the geologist does not have to put fragmentary data 
together and grope for the general facts of which they form 
part, but is able to see all the parts combined in nature in visi- 
ble wholes. Nothing need be left for doubtful interpretation 
where everything can be seen; and with the facts of structure 
conspicuous and beyond question, the mind is left free to search 
for causes. 
The facilities for the study of single, simple displacements, 
isolated from other phenomena of the same order, are equalled 
by those for the study of eruptive mountains which are at once 
simple, isolated, and dissected by erosion. 
To the student of stratigraphy are offered continuous expos- 
ures of great length. 
To the student of erosion are exhibited the most distin- 
guished monuments of its action; and he is given an opportu- The Colorado Plateau Province. 
27 
nity to partially isolate certain of the conditions which con- 
trol the rapidity of erosive action, by viewing their influence 
where that influence is at a maximum. 
No attempt has been made in this brief review to indicate 
the entire range of the subjects that will interest the geological 
student of the region. It was proposed rather to call attention 
to those categories of phenomena which give greatest promise 
of affording contributions to the body of principles which con- 
stitute the science of geology,—as distinguished from the phe- 
nomena which will merely enlarge the body of facts upon which 
its established principles are based. The progress of geological 
exploration has compassed so small a fraction of the earth’s sur- 
face that the aspect of the science is modified, in greater or less 
degree, by the addition of each important mass of facts; and 
when the contribution from the Plateaus shall have been made, 
I am confident that its record will find a place in the history of 
geological progress. 
Already the field has yielded to its students results which 
are new to them, and which are probably new to the world of 
science. Among them are a type of uplifted mountains, a 
type of eruptive mountains, a theory of waterfalls, and a classi- 
fication of drainage systems.