- u DEPARTMENT OF AGRICULTURE ARTESIAN WELLS I Tn.\ I II I GREAT PLAINS; THE REPORT OK A GEOLOGICAL COMMISSION APPOINTED TO EXAMINE A PORTION OF THE GREAT PLAINS EAST OF TUP ROCKY MOUNTAINS, AND REPORT UPON THE LOCALITIES DEEMED MOST FAVORABLE FOR MAKING EXPERIMENTAL BORINGS. VTA 8HIXGTOX: GOV E R N M E N T P R I N T IMr F F I C E IS 82. I J-. 1 ^DEPARTMENT OF AGRICULTURE^fttf*-^ ARTESIAN WELLS .■>-," ITiiX THE GREAT PLAINS; BKING THE REPORT OF A GEOLOGICAL COMMISSION APPOINTED TO EXAMINE A PORTION OF THE GREAT PLAINS EAST OF THE ROCKY MOUNTAINS, AND REPORT UPON THE LOCALITIES DEEMED MOST FAVORABLE FOR MAKING EXPERIMENTAL BORINGS. /■" WASHINGTON: GOVERNMENT PRINTING OFFICE. 18&2. 5150 ^cA% ^ LETTER OF TRANSMITTAL, Hon. George B. LorinG, Commissioner of Agriculture : Sir : Having been appointed by yon a commission to make scientific examination of certain arid lands of the United States east of the Rocky Mountains, for the purpose of indicating suitable localities for boring experimental artesian wells, we have the honor to present the accom- panying report of the results of our examinations during the season of 1881. The region within which we were expected to operate, as indicated by your general instructions, is a very large one, the area and boundaries of which we understood to be as follows : All that area which lies be- tween the meridian of 102° on the east and the base of the Rocky Mountains on the west, and between the northern boundary of the United States on the north and the southern boundary of the same on the south. , The season was so far advanced before we were able to begin our labors in the field that the necessity for confining them during the comparatively short time that field work would be practicable to a limited portion of the great area above indicated became at once ap- parent. Accordingly we selected that portion of Colorado which lies east of the Rocky Mountains as the field of our labors for the short sea- son that remained, and received your approval of the same. Under ordinary circumstances it would have been impracticable for us to make such an examination of this large district within a time so limited as would warrant a conclusive report upon the subject required. But owing to the fact that both of us had, on former occasions, examined large portions of this district in such a manner as to make the results available for the purpose of this commission, we have been able to arrive at conclusions that, so far as a belief in their approximate accuracy is concerned, are to a considerable degree satisfactory to us. It would have been much more agreeable to us if we had found our- selves able to make a report which would encourage a confident hope of abundant success as the result of such experimental borings within this district as were contemplated by the act of Congress authorizing the work upon which we have been engaged. The conclusions we pre- sent are, however, those to which we have felt ourselves compelled to arrive, and in support of those conclusions we also present the data upon which we have based them, that others may judge of their accuracy or fallacv as well as we. 4 ARTESIAN WELLS UPON THE GREAT PLAIN'S. We desire in this connection to say that while a large part of the facts and conclusions which we present in our report will apply with equal force to the whole arid region of the plains, we have purposely confined our report to the region we have designated. Success or fail- ure in artesian borings depends primarily on geological structure, and that structure may be more favorable in places outside of our district than we have found it to be within it. A correct knowledge of that structure being attainable only through a careful investigation by skill- ful geologists, we venture to recommend that all future work of this kind be assigned to the United States Geological Survey. Respectfully submitted. C. A. WHITE, SAMUEL AIGHKY, Commissioners. Washington, 1>. C, February 7, L882. ARTESIAN WELLS UPON THE GREAT PLAINS. REPORT OF THE COMMISSIONERS. I N T K O I) 1' C T OK V R E AI A K K S . While this report embraces a coDsideration of only a small part of the great arid area of the West, the district to which it refers, namely, that portion of the State of Colorado which lies east of the Rocky Mount- ains, is nevertheless of considerable size, embracing' as it does about 40,000 square miles. The principal features of this large district, as well as those of the large areas that adjoin and are continuous with it both upon the north and south,. are very simple, the whole region referred to being, in fact, one of the well-known great plains of the earth, the general uniformity of which is seldom broken by any considerable local elevation of the sur- face. It is, however, bounded on the west by the abruptly rising prin- cipal chain of the Rocky .Mountains, some of the peaks of which reach an altitude of over 14,000 feet above the level of the sea. By reference to the lists of elevations along the lines of railway that traverse it from east to west, the surface of our district is found to have a general slope to the eastward from near the base of the Rocky Mountains of from 10 to 12 feet to the mile. Roughly calculated, the average elevation of the district above the level of the sea, exclusive of the locally elevated areas near the mountains, which we have designated as Tertiary high- lands, is about 4,450 feet; the lowest point within its borders, which is where the Arkansas River crosses its eastern boundary, is 3,120 feet. In consequence of this easterly slope of the surface, the two principal rivers of the district, the Arkansas and South Platte, traverse it in an easterly direction, the distance from the base of the mountains to the eastern border of the district being fully 150 miles. After assuming this almost easterly course upon the plains, both these rivers not only receive almost no accession to their volume of water during the summer season, but their volume in summer time is often actually lessened by evaporation and absorption as they flow to the eastward upon the plains. Their constant supply is derived from their numerous branches, which head among the Rocky Mountains. These facts, together with others which will be brought out upon the following pages, show the great aridity of the district during at least a portion of each year. 6 ARTESIAN WELLS UPON THE GREAT PLAINS. During the prosecution of our investigations we found it convenient to divide the general subject under three principal heads, namely: (1) the general topography and surface features of the district; (2) the geological structure of the district and of the adjacent mountains; and (3) the primary sources of water supply in and around the district. In the presentation of our report we shall follow the same divisions of the subject, and add (4) a brief history of the attempts that have been made by various parties in and near the district to procure water by means of artesian borings, and (5) a statement of our conclusions and recommendations. We shall also add, as appendices to the main subject of* our report, (6) a statement of the results of incidental observations concerning availa ble sources of water supply within the district other than that which may be hoped for by means of artesian wells; and (7) the special report which we have already presented upon the artesian boring that has been made near Fort Lyon, Colo., under the auspices of the department. TOPOGRAPHY AND SURFACE FEATURES. This district being a portion of the great plains, its topography, as before indicated, is very simple, the surface of the plain within the limits of the district having, as has already been stated, a general slope to the eastward of from 10 to 12 feet to the mile; but this, while it is quite sufficient for complete and rapid surface drainage by means of its rivers and tbeir tributaries, is too slight to be detected by the eye. The great chain of the Kocky Mountain system, made up of a compact mass of crowded peaks and gorges, rises almost as abruptly as a wall along the whole western border of the district. Within that portion of the great continental mountain chain, towering above the others, are some of the most noted peaks to be found within the limits of the United States; and no part of that great chain is more compact and character- istic than is that which borders the district upon which we here report. At the base of and closely against the eastern mountain front is a com. paratively narrow fringe of foot-hills, the larger ones of which would elsewhere be regarded as mountains, but in the presence of the mighty members of the chain they hold a subordinate place. While even the higher peaks of the great chain do not reach an elevation that in full exposure to the influence of the sun would be above the true line of per- ennial snowfall in that latitude, there is a multitude of limited perennial snow-fields in the less exposed places among those mountains, some of which have an elevation of 3,000 or 4,000 feet less than that of the higher peaks; and dwellers in the adjacent plains are never out of sight of the white glitter of these interesting features of mountain scenery. From thgse numerous small snow-fields and the comparatively abundant rains that fall upon the mountains and not upon the plains, in summer time, multitudes of rivulets arise. These rivulets gather and unite in the gorges and find their way out upon the plains in the form of rapid streams, ARTESIAN WELLS UPON THE GREAT PLAINS. 7 all of which are quickly gathered together to form, respectively, the two principal rivers of the district, the Arkansas and South Platte. In consequence of retreating bends to the westward in the course of the eastern front of the mountain range towards the southwestern por- tion of our district, a part of the mountain streams which unite to form the Arkansas River do not before their confluence enter the proper limits of the district; bnt those which unite to form the South Platte all effect their continence upon the plains, not only within the district, bnt within a distance eastward from the foot-hills of the mountains not exceeding twenty miles. All these mountain-born streams are constant and copious in their flow, even all through the summer, but some of the smaller ones which make their exit from the mountains and foot-hills with a copious flow of water have their volume greatly diminished, and in some cases wholly obliterated, upon the plaius in summer-time by the rapid evaporation which occurs there in consequence of the dryness of the earth and atmosphere. Also, the numerous streams which are rep- resented upon the maps in common use as tributaries of the South Platte and Arkansas, respectively, and which have both their source and debouchment upon the plains, are all either dry during the summer- time or they are reduced to a few isolated pools. During this portion of the year one may traverse these channels from mouth to source, and find a part of them as dry throughout their entire length as are the plains on either side of them; or, approaching the mountains in some of these dry channels, he may gradually come upon constantly flowing streams of pure and good water which is all lost long before the mouth of the stream is readied. During a portion of the spring and autumn, however, all the streams of the plains are broad and strong torrents of muddy water. Traversing the great plains, of which our district forms a part, the general aspect of the surface is found to be similar to that of the great prairie regions of the States of the Upper Mississippi Valley. It is utterly treeless every where, except that a fewclumpsof cotton woods and willows are found at the river margins, and rarely some scattered cedars occur in rocky ravines that sometimes cnt the valley sides. Grasses of the most nutritious character for grazing, and various other herbaceous plants prevail, but vegetation does not cover the surface nearly so thickly as it does upon the prairies. The frequent and often abundant prevalence of cactus and other plants which are characteristic of arid regions also gives a desert-like aspect to the whole landscape in summer- time, when the fresh vegetation of spring has withered away. The soil of the plains is evidently much the same in character as that of the prairies, and tests that have been made of its capach^y show that it only needs the seasonable application of water to make it quite as fertile. In the vicinity of the mountains within this district we find two areas which have a distinct and considerable elevation above the great general level of the plains, and which, while they are near the foot-hills of the 8 ARTESIAN WELLS UPON THE GREAT PLAINS. mountains, are quite distinct from them. One of these elevated areas lies north of the South Platte and between that river and Lodge Pole Creek. The other, which is much the larger area, lies to the southward of Denver, and between that city and Colorado Springs. The limits and characteristics of these Tertiary deposits will be explained under the head of geology. As we shall have occasion to make further ref- erences to these limited elevated areas as separate from the great gen- eral surface of the plains, we shall in this report designate them as the Tertiary Highlands ; but it is proper to remark that this name is pro- posed not for general use, but only for conventional use in this report. The borders of the more northerly of these Tertiary highlands are generally so well denned that they are readily recognizable from a dis- tance on the plains, because they often assume the form of more or less abrupt bluffs, from 100 to 200 feet high, and they are sometimes made still more conspicuous in the monotonous landscape by occasional clumps of cedars or scattered trees of that kind which grow upon their crests or slopes. The more conspicuous of these bluffs have received local names, such, for example, as the a Chalk Bluff's," just upon the northern boundary of our district and some 25 miles southeastward from the city of Cheyenne. The more southerly of the Tertiary highland areas is the larger and much the more elevated, the higher portions reaching an elevation of 600 or 800 feet above the general level of the adjacent plain. But its boundaries are not so clearly denned by precipitous bluffs as those of the northern area ; its general surface is more uneven, being divided by erosion into numerous hills and ravines ; and considerable portions of the area are occupied by somewhat scattered small bodies of timber, mostly pines and cedars. In some sense these hills partake of the char- acter of foot-hills of the adjacent mountains, but they are separate from and lie just east of the foot-hills proper. These Tertiary highlands are specially noticed in this report, not so much because they are conspicuous topographical features of that strongly featured region as because in the letter of instructions which we received when entering upon the work the wish was expressed that we should learn as far as practicable the probabilities of obtaining water by means of borings of comparatively little depth in the superficial and Tertiary deposits. The character of the Tertiary deposits will be further elucidated under the head of geology of these districts, and the bearing of their structure upon the special subject of this report will be con- sidered under the head of conclusions. AvSide from these Tertiary highlands, there is nothing in our large dis- trict to break the monotonous undulation of the general level of the plain, except the shallow and usually broad valleys of the water-courses, all of which have a good degree of uniformity of character throughout their entire length; but the sides of the smaller valleys blend with the undu- lations of the plains at their upper portions. Like the higher surface of ARTESIAN WELLS UPON THE GREAT PLAINS. 9 tbe plains, the valleys are all destitute of trees, with the unimportant exceptions that have before been noticed. The valleys of the South Platte and Arkansas are similar to each other in general characteristics across the whole breadth of the district. Their sides slope so gently down from the uplands or higher general level of the plain that it is almost everywhere difficult to say where the valley sjde ends and the higher land of the plains begins. There is usually a considerable space at the bottom of the valley upon one or both sides of the river which to the eye appears nearly level, but which, as a rule, has a gentle slope towards the river, sufficient for its complete drainage. These valley bottom lands are generally of such a character and breadth that they would make admirable farms if they were only supplied with water at seasonable times. Upon the lowermost of these bottom lands the moist- ure derived from their proximity to the river is sufficient for the abun- dant growth of valuable grasses, which are now annually cut for hay. GEOLOGY OF THE DISTRICT. The geology of that portion of the great plains which constitutes the district upon which this report is based, like its topographical features, is very simple. The strata which underlie it have one broad but very gentle general dip to the eastward, away from the mountain chain, which dip is practically coincident with the general slope of the sur- face, which has already been described. Furthermore, this dip and the general slope of the surface to the eastward both coincide with the general slope of the two principal rivers of the district, the South Platte and the Arkansas, the course of both of which upon the plains is in the same direction. The general features of the geology of this district and that of the adjacent mountain region are well shown in the atlas of Colorado which has been published by the United States Geological Survey of the Territories. A copy of a part of one of the sheets of that atlas accompanies this report, containing such additions by us as we have thought necessary for the elucidation of the subject in hand. Certain of the minor geological details which cannot be clearly shown upon the map, especially the secondary undulating dips of the strata of the plains, which we regard as having an important bearing upon the question of artesian water supply, were worked out by us during the past season. The great axial mass of the Rocky Mountain chain which lies adja- cent to our district consists of unstratified arclnean rocks, a large part of which are granitic in composition. The plains in the region which embraces the district upon which we report are underlaid by different formations of stratified rocks, which formations in the vicinity of the mountains are known to range in the geological age from the Triassic to the Tertiary, inclusive. At certain places among the mountains and foot-hills which adjoin our district upon the west a few isolated por- tions of Silurian and Carboniferous formations have been discovered, but 10 ARTESIAN WELLS UPON THE GREAT PLAINS. the development of tbese paleozoic rocks is so slight that for oar pres- ent purposes we do not think it necessary to make anything more than incidental reference to them. All the other formations here referred to, except the Tertiary, are abruptly flexed up against the arclncan axial nucleus of the mountains, and enter largely into the structure of the narrow range of foot-hills of those mountains. Many of these foot-hills, being composed of the upturned harder and softer stata of the forma- tion just mentioned, have been so shaped by erosion that they form more or less sharply angular longitudinal ridges, which are commonly desig- nated as hog-backs. It is among the foot-hills, where the stratified rocks are up turned, that the latter are to be seen and studied to best advan- tage, because out upon the plains the higher formations of the series cover the next underlying ones successively, and, except at occasional exposures, even the uppermost ones are covered, as with a mantle, by the superficial deposit or debris of the plains. This debris is reallj- that w T hich has been derived from the easily disintegrated underlying rocks, and which, mixed with gravelly fragments that have been derived from the mountains, constitutes the soil and subsoil of the plains. The Tertiary strata of this district were no doubt once flexed up against the mountains like those of the formations which underlie them, but perhaps to a considerably less extent than those; but they have been removed by erosion from those rocks which once underlaid them and now enter into the structure of the foot-hills. Those Tertiary rocks no doubt also once extended far out upon the plains, covering large areas there; but with the exception of the two limited areas that we have already described as the Tertiary highlands, which are composed of those strata, they have all been removed by erosion from the plains portion of our district also. The following is a tabular statement of the whole series of forma- tions of stratified rocks which pertain to the district here reported on, except the small Silurian and Carboniferous deposits which have before been mentioned. Opposite the names of each group is placed the ap- proximate thickness in feet which they respectively attain in the western part of the district, the measurements having been taken where the strata are upturned against the mountains: Feet. Tertiary 200 to 1, 400 Laramie 200 to 1, 000 ( Fox Hills Groups 1, 200 to 1, 500 ^ Cretaceous^ Colorado Groups 800 to 1,000 >2,250 to 2,900 l Dakota Groups 250 to 400J Jurassic 400 to 800 Triassic 1, 500 to 2, 000 Total t 4, 550 to 8, 100 • Tertiary deposits.— -The deposits which we have designated as of Ter- tiary age are not now, as before stated, flexed up against the mountains, but their western borders are very near to the foot-hills. The more ARTESIAN WELLS UPON THE GREAT PLAINS. 11 northerly of the two areas within the district lies just upon its northern boundary, and extends out upon the plains some 75 or 80 miles to the eastward from the foot-hills within the district, and still further east- ward in the district which lies just north of it. The more southerly of the two Tertiary areas is some 50 miles across from east to west, and about 10 miles across from north to south. The strata of both these Tertiary deposits are all approximately level, or they dip slightly to the eastward, like those upon which they rest. While the strata of both the northern and southern Tertiary high- lands here referred to undoubtedly belong to the Tertiary period, and are as undoubtedly of fresh- water origin, it is understood by us that those of the two areas, respectively, are not referable to oue and the same epoch of the Tertiary period. But they both rest directly upon the Laramie Group, and the lithological character of the one being closely like that of the other, they are practically one for our present purpose, which is only to show the bearing of the geological structure of the district upon the question of water supply by artesian boriugs within its limits. The areas occupied by those Tertiary deposits are represented by the spaces on tke accompanying geological map which are colored plain yellow and marked by the letter T. These Tertiary deposits of both areas are largely made up of friable sandstones, sandy shales, and conglomerates, with very few clayey layers, and also some strata of more or less compact sandstone. They contain comparatively few layers that are impervious to water or that would materially obstruct its percolation through the whole formation. Laramie Group. — This group of strata constitutes the coal-bearing formation of Colorado east of the Rocky Mountains. It has, in our district, a maximum thickness of about 1,000 feet : but over a large part of the district its strata are reduced by erosion to 100 to 200 feet in thickness, and upon the borders of the river valleys it has been thinned out entirely by erosion, which has also here and there laid bare the underlying Cretaceous strata. This formation is shown by the character of its fossil remains to have been of brackish- water origin; and we regard it as holding a transi- tional position between the strata of Cretaceous and Tertiary periods proper, in its biological characteristics partaking of both. It is quite uniform over the whole district in its lithological characteristics, being made up largely of clayey strata, which are more or less sandy, and occasional sandstones and sandy shales, all of which are usually more or less calcareous. Therefore, as a whole, it is evidently a formation through which water could work its way slowly if at all by percolation, although a few of its layers are so sandy and slightly compacted that water might apparently percolate through them with some facility if it were not obstructed by the impervious layers above and beneath them. The strata of the Laramie Group occupy a greater portion of the area of the district immediately beneath the superficial deposit than those 12 ARTESIAN WELLS UPON THE GREAT PLAINS. of all the other formations together; in consequence of which, and of its lithological characteristics as already described, it has a very im- portant bearing upon the questions to be discussed in this report. The area occupied by the Laramie Group is shown by the spaces upon the accompanying geological map which are colored by green, circular dots on a yellow ground and marked by the letter L. Although the flexed condition of the strata of this group, in the immediate vicinity of the mountains, shows that they were all originally upturned to an equal extent with the others which underlie them, they are now not often found to enter into the structure of the foot-hills proper. This is without doubt due to the fact that the Laramie strata, being as a rule comparatively soft and friable, have been removed by erosion wherever they have been prominently exposed by reason of the upward flexure, while the harder strata of the formations beneath them remain in the form of the prominent hog-backs among the foot-hills that have already been described. Cretaceous formations. — The strata of marine origin which are refer- able to the Cretaceous period are in Colorado divisible into only three distinct groups,* namelj , the Fox Hills or Upper, the Colorado or Mid- dle, and the Dakota or Lower. All three of these groups are flexed up together against the mountains, and all three of them enter to some ex- tent into the structure of the foot-hills. Upon the plains the Cretaceous strata, like all the others, being in nearly a horizontal position, do not produce any prominent features in the landscape. Next to the Laramie Group, the strata of these three Cretaceous groups occupy a greater portion of the surface of the district than any other. Upon the plains they are exposed in the valleys and vicinity of the rivers and their larger tributaries ; and the areas which they oc- cupy are represented by the spaces on the accompanying geological map, which are colored green and marked by the letters Cr. The lithological characteristics of these three groups, as well as those of the others yet to be noticed, have an important bearing upon the question of artesian water supply. The Fox Hills Group is composed in large part of bluish clayey strata, somewhat arenaceous for the upper portiou, and sandstones and sandy shales for the lower portion j but among the latter are many soft and some clayey layers. The Colorado Group is composed very largely of argillaceous shales, and toward the base these shales are somewhat firm and calcareous, and often fissile. This description applies more particularly to the northern portion of the district, but in the southern portion this group is much more calcareous than in the northern, and near its upper portion there are many layers of firm, regularly-bedded, gray limestone. As a whole, the Colorado Group is one that will evidently not allow the free perco- * Sec Annual Report U. S. Geol. Sur. Terr, for 1876, p. 29. ARTESIAN WELLS UPON THE GREAT PLAINS. 13 latioo of water through it. Indeed, it is evident that this group would present great obstruction to the percolation of water. The Dakota Group is.largely made up of coarse, rough layers of more or less firm sandstone, and although a considerable portion of it is soft, and sometimes clayey, it is perhaps more pervious to water than any of the other formations which underlie the district. These saifdstones are therefore regarded as presumably water-bearing strata. It is one of the most uniform in its lithological characteristics of all the Cretaceous groups of North America. Jurassic. — This is one of the thinner of the formations which underlie our district, averaging only 500 feet at its western border, where the formation is upturned among the foot-hills. It is composed mainly of argillaceous material, in the form of clayey and somewhat sandy shales, with occasional beds of impure limestone and sometimes small deposits of gypsum. As a whole, therefore, this formation is also one of the most impervious to water. Although it is evident that these Jurassic strata underlie at least all the western portion of our district, none of them are- exposed at the surface within its limits, but the whole formation is up- turned among the foot hills, where, being composed of easily eroded material, it usually occupies the longitudinal valleys which are bordered on either hand by the hogbacks of the Dakota and Triassic groups re- spectively. The limited area within which the strata of this group are exposed at the surface is too small to be represented alone, and it is therefore included in the very narrow, irregular, interrupted purple stripe upon the accompanying geological map, marked by the letters J. T., which also includes the Triassic strata. Triassic. — Although — as is shown by the narrow space upon the map which has just been mentioned — this formation occupies a very narrow area of the surface, it is the thickest, and in some respects one of the most important of the formations which we have occasion to discuss. It has an average thickness of about 1,700 feet. It is composed mainly of sandstones, which are often coarse, and which sometimes alternate with layers of conglomerate. The nearly uniform red color that prevails throughout the formation almost everywhere has caused the common name of u Red Beds" to be applied to it. The sandstone layers are usually harder than those of the other formations, but still they are not very dense, and those alternate with softer layers, some of which are argillaceous. The greater part of the strata of this formation being harder than those of the other formations that have been described, they often form large and conspicuous hills among the foot-hills, many of which are in the form of huge hogbacks. Like the Jurassic, none of the strata of the Triassic formation are ex- posed upon the plains, and therefore not within the limits of our dis- trict, and the foregoing description has been drawn wholly from the strata as they are seen among the foot-hills. That the formation really 14 ARTESIAN WELLS UPON THE GREAT PLAINS. does extend far out from the mountains under the plains is, in our opinion, not to be questioned, and that the strata have the same gen- eral characteristics there may be legitimately inferred from the fad that those characteristics are very uniform wherever the formation is found at the surface on both sides of the Rocky Mountains. These inferences a»e also confirmed by the result of the boring that has been made near Fort Lyon. This formation, composed as it is of sandy rock, would, if its strata were loosely compacted and regularly bedded, no doubt allow the ready percolation of water; but many of the strata are often found to be very dense, and many are also so argillaceous as to render it unlikely that much water could percolate through them. But the formation is a very thick one, and many of the strata would doubtless be permeable wherever a water supply may exist in contact with them. Therefore we shall regard it as like the Dakota sandstone — a presumably water- bearing formation. The formations that we have here described constitute the whole series of stratified rocks that are known to underlie the district. The small local deposits of Silurian and Carboniferous strata, which are in a few places found among the foot hills and the adjacent mountains, suggest that the same formations exist, to some extent at least, beneath the surface of our district, and consequently beneath the Triassic rocks. Possibly the last-named strata may there, at least in part, rest directly upon the arclnean rocks, as they are seen to do in most cases at the foot-hills; but in any case the arcluean rocks doubtless lie at a depth beneath the plains that will be beyond the reach of any borings that it will be found expedient to make there. The only method by which the actual presence beneath the surface of the plains of any series of rocks older or lower than the Cretaceous can be demonstrated is by artesian borings. We may, however, to some extent, draw inferences as to the probable presence or absence of certain formations, respectively, beneath given portions of the district. For example, it is probable that beneath its eastern portion the Silurian and Carboniferous rocks are present and more fully developed there than they are at the foot of the mountains, because those rocks, as well as those of Devonian age, are well developed in the valleys of the Mis- sissippi and Lower Missouri Rivers. Again, the Jurassic and Triassic strata, especially the latter, are, as has already been shown, well de- veloped along the western border of the district; but neither of these formations are known to exist in the Mississippi and Lower Missouri Valleys, nor at any point between them and the eastern base of the Rocky Mountains. Therefore the inference is plainly correct that those forma- tions have thinned out somewhere beneath the plains, and it is possible that they may have done so before they reached the eastern border of the district. It is also probable, or even practically certain, that the Cretaceous strata, except the Dakota Group, also materially dimin- ARTESIAN WELLS UPON THE GREAT PLAINS. 15 ish in thickness as they extend to 'the eastward. The same is evi- dently true of the Laramie Group, which doubtless thins out entirely in Western Kansas and Nebraska. If, therefore, we should make a boring' upon the plains within a short distance eastward from the liocky Mountains we should expect, from our knowledge of the character and order of the strata as we find them flexed up against the mountains, that the drill would pass through the same formations and in the same order. The boring that has been made at Fort Lyon, Oolo., under the auspices of the Agricultural De- partment, has really proved that this condition of things exists beneath the plains, 100 miles eastward from the mountains. It is unfortunate, however, speaking from a geologist's stand-point, that the boring there was not carried down until the Triassic rocks were passed, instead of stopping, as it did, in those strata. This act, however, was plainly justified from an economic standpoint, as we have shown in our special report upon the subject. If we were to make a boring* upon the plains near the eastern bor- der of our district, which is some 150 miles eastward from the base of the mountains, we might, from our knowledge of the broad, geographical extent of those formations, reasonably expect to find all the formations present there, from the Laramie to the Dakota Group, inclusive; and perhaps also the Jurassic and Triassic. It maybe, however, that the two latter formations have entirely thinned out before reaching so far eastward ; and it is quite certain that all the others, except the Dakota Group, which is known to exist in full force in Kansas and Nebraska, would be found to have become much thinner than they are at the base of the mountains. The question of the thinning or thickening to the eastward or westward of the formations that underlie the plains is a matter of practical importance, as well as of geological interest, as will be seen by our remarks under the head of conclusions. In this connec- tion it should be stated that we have good reasons for believing that as a whole the stratified rocks which underlie the plains are much thinner at the eastern than at the western border of our district. The un stratified arch se an rocks of the Rocky Mountain region, and which it is assumed deeply underlie our whole district, appear at the surface within those areas which on the accompanying geological map are colored with a pink tint, and are marked with the letter M. They are such as are often designated as metainorphic rocks, and are similar in character to those which underlie the lowest stratified rocks elsewhere, so far as that character relates to the question of artesian water supply That is, not being stratified, we cannot calculate upon the course that water will take in passing through them, nor, indeed, can we think it probable that water will find its way by percolation through them beneath the surface to any considerable horizontal distance from the place where it falls from the clouds. It is true that springs are more or less frequently met with among that portion of the Rocky Mountains which 16 ARTESIAN WELLS UPON THE GREAT PLAINS. lies adjacent to our district, issuing from the arclnean rocks, and water is also frequently so abundant in the deeper mines of those mountains as to greatly impede the working- of them. This water is without doubt, in every case, derived from the rains and snows that fall upon the mountains in the immediate vicinity of the springs and mines referred to, and it has made its way to these outlets through the numerous irregular fissures which prevail in such rocks. These fissures, being irregular in character and direction and the rocky masses through which they pass being without stratification, the courses which those fissures may take cannot be calculated. Their irregular character, and the well-known character of the kind of rock through which they pass, renders it certain that however numerous these fissures may be they do not form continuous channels for the conduc- tion of water to any considerable horizontal distance beneath the sur- face. Whilje it is probable that water may percolate through the great mass of the unstratified rocks of the Rocky Mountains, and that some water may find its way thus and by means of fissures beneath the stratified rocks upon the plains in the immediate vicinity of the mount- ains, it is not to be expected that even small quantities of water should be thus conveyed beneath the plains to any considerable distance from its mountain sources. Practically, then, we think we are justified in regarding the unstratified arch a3 an rocks as forming an impervious base to the stratified series of rocks within which, if anywhere, we may hope to obtain a water supply upon the plains by means of artesian borings. We have already referred to the gentle general dip to the eastward from the base of the mountains of all the formations of stratified rocks which underlie our district. Although neither this easterly general dip nor the modifications of it which exist in various parts of the district are discernible to the eye, our acquaintance with the lithological and paleontological characteristics of the strata which are exposed at dif- ferent points on the plains throughout the district, taken in connection with several series of elevations above the level of the sea that have been referred to has enabled us to reach conclusions that would not have been otherwise attainable. A portion of those series of elevations we have obtained from (Taunett's published lists, and others have been furnished to us by the officers of the Union Pacific and Burlington and Missouri River Railroad Companies respectively. The modification of the general eastwardly dip of the strata, of the district which has been referred to consists of gentle undulations of the strata, which are so very broad and slight that they coiilo* not be detected, except by means of the railroad levelingsthat have been referred to and the surface slopes of the Arkansas and South Platte rivers. We have used the surface slopes of these rivers as base-levels by which to note the rise and dip of certain recognizable and persistent strata, above and below those levels, in the banks of the Rivers respectively. By means of these methods of observations we have ascertained that the Arkansas ARTESIAN WELLS UPON THE GREAT PLAINS. 17 and South Platte Rivers each runs upon a very gentle anticlinal axis of the underlying strata, which axis extends across nearly or quite the whole breadth of the district. Consequently, there is a very gentle and very broad synclinal axis between the two rivers. The distance be- tween the two rivers at the eastern x>ortion of our district is about 180 miles, and the extent to which the strata are flexed downward between them there is estimated at about 400 feet. The gentle undulations along north and south lines which the strata of the plains are found to possess, and which lie at right angles with the broad east and west anticlinals and synclinals that have been mentioned, have been explained in our special report upon the boring which has been made near Fort Lyon, Colo., under the auspices of the Department of Agriculture, and which is added to this report in the form of an appendix. No such undulations have been observed along the valley of the South Platte, and although they may exist elsewhere in the district than in the valley of the Arkansas River their presence has not been detected. Those undulations, as shown in the report re- ferred to, have an important bearing upon the question of artesian water supply in the region of that valley. It will also be seen in the sequel that the broad synclinal between the two rivers of the plain, which has been explained, although so slight in the amount of its depression, is a very important geological feature in relation to the subject of this report. The superficial deposits of the plains. — Before closing these remarks upon the geology of the district, further mention should be made of the superficial deposits or debris of the plains. This material, as already stated, is derived mainly from the immediately underlying stratified rocks, by their disintegration; but scattered among it, even as far out from the mountains as the eastern border of our district, are small fragments of granitic rock, which by its character is plainly seen to have been de- rived from the archaean rocks of the mountains. It was probably trans- ported thence by the action of ice during the glacial epoch. This fine angular gravel sometimes, but seldom, is found in perceptible local accu- mulations upon the higher surfaces of the plains, but it is more percepti- ble in the valleys. Indeed, the larger valley bottoms are apparently all underlaid by material which consists largely of this loose drift-gravel. "This condition of the ground makes the procuring of ordinary wells of good water at moderate depth in the larger valley bottoms of the dis- trict an easy matter in almost all cases. PRIMARY SOURCES OF WATER SUPPLY. In such districts as lie below the level of great lakes or other bodies of water that may exist in their vicinity, it is possible that an artesian water supply may be derived from such a source. In the region within which our district is located, however, no such source of supply can be considered, because no such bodies of water exist there nor in the regions round about, and no rivers traverse the district other than those 5156 2 18 ARTESIAN WELLS UPON THE GREAT PLAINS. which have their rise in the adjacent mountains. Therefore, the only primary source of water supply to be considered in this report is that of rainfall. For the purpose of showing the amount of water that falls upon the surface in and around our district, the following tables- of rainfall are given, which have been compiled from the published reports of the United States Signal Office, the publications of the Smithsonian Institu- tion, and Powell's Report on the Lands of the Arid Region of the United States. So few stations of observation have been located upon the more arid portions of the great plains that these tables do not really show the full extent of the contrast between those portions and the more favored region immediately to the eastward as regards the amount of rainfall, but these data are the most instructive of any that we have found available for our present purposes. Table No. 1. — Annual and monthly rainfall at certain points in Colorado, Wyoming, Ne- braska, and Kansas, for the fire i/ears ending June 30, 1879. Localities. Pike's Peak . Denver 3. 'J.') Cheyenne 1.87 * North Platte. * Dodge City . . Omaha Leavenworth.. 1874. "a »-5 ■r. M z 0Q s o O "November. 6.00 3.72 2.31 1.80 0.36 0.22 3. 'J.') 0.68 1.34 0.01 0.18 0.17 < 1.87 0.44 0.93 1.86 0.04 0.16 2. 48 2.42 0.85 1.46 0.57 0. 34 2.28 2. 92 0.94 0.22 0. 23 0.05 0.54 2.08 7.18 1.45 1. 05 0. 54 3.23 1.72 5.50 1.49 3.46 1.35 18 75. P a e A 1 hi 0.76 3.38 0.42 0. 24 0.12 0.26 0.23 0. 50 0.60 0.06 0. 26 0.10 0.51 ,,, 1.03 0. 39 0.23 0.40 0.04 1.24 2.50 0.92 2.24 0.50 6.21 0.72 3.06 1 67 2.08 1.94 1.20 1.69 2. 26 4. 25 3. 53 1.70 0.43 0. 29 1.62 0.73 10.95 3.85 21.40 15. 24 8.00 21.24 11.61 33. 11 Pike's Peak. Denver I Cheyenne North Platte ... Dod^eCity Omaha Leavenworth... 1875. 1876. 8.13 3.52 3.20 0.38 1. 54 0.98 0. 85 0.61 2.03 1.04 4.73 2.88 4.32 1.97 2.89 0.22 1.28 0.59 0.21 0.11 1.80 1.22 8.57 1.10 4.47 2.12 1.34 0.60 0.84 0.03 0.02 0.06 0.54 0.23 2.50 0.10 1 2.12 0.66 1.40 0.14 0. 52 0.09 0.09 0.13 0.49 0.51 2. 97 0.49 , 3.28 2.06 1. 32 0.06 0.00 0.09 0.00 0.05 3.59 0.16 1.15 1.53? 10.01 7.77 2.55 1.16 0.13 1.00 0.22 0.40 3.18 2.65 2. 07 3.47 8. 82 3.73 1.97 0.72 0.39 2.60 ,« 0.20 5.78 7. 65 6.78 5.7! 29 89 24.28 12.85 9.61 14. 29 34.