# The New International Encyclopædia/Rocky Mountains

Edition of 1905. See also Rocky Mountains on Wikipedia; and the disclaimer.
ROCKY MOUNTAINS. A name here used to indicate the assemblage of mountain ranges which form the ‘backbone’ of North America. They begin at the south in Central Mexico, and extend northward across the United States and Canada to near the coast of the Arctic Ocean. On the east they are bordered from near Vera Cruz, Mexico, to the valley of the Mackenzie, by the Great Plateaus, or Great Plains as more commonly termed; and on the west, within the United States, by the Great Basin region which reaches from the head of the Gulf of California northward into Canada, and separates them from the Sierra Nevada and Cascade Mountains. The west border in Canada is less well known and as seems probable less sharply defined than is the portion just referred to, but may be taken at least provisionally as coinciding with the west border of the Gold Mountains of Canada.
The unsatisfactory condition of the nomenclature at present applied to the larger physiographic features of North America is illustrated above by the rather vague limits it is necessary to assign to the Rocky Mountains. The same condition is also shown by the fact that in Canada the term Rocky Mountains is restricted to the east range of the series of uplifts to which it is applied in the United States. To the west of the range thus designated, in Canada, and separated from it by a broad valley some 700 miles long, trending north and south, are the Gold Mountains, consisting principally of the Selkirk, Purcell, Columbia, and Caribou ranges. The term ‘Canadian Rockies’ is in current use, however, and includes all of the mountains in Canada, which are a direct northward continuation of the Rocky Mountains of the United States.
To the south of the United States the Rocky Mountains include the tableland of North-central Mexico, with its numerous rugged mountain ranges and intervening valley, all of which trend in a generally north and south direction.
The length of the Rocky Mountain chain from north to south is some 4000 miles, and its width between 400 and 500 miles. Within its borders are several mountain systems, as will be shown below, and a large number of individual ranges,
together with several large plateaus, numerous valleys, ‘parks,’ cañons, etc., as well as multitudes of peaks, ridges, mesas, and buttes. In fact, it contains typical representatives of nearly every known topographic form. Considered in reference to origin, the topographic forms mentioned include elevations produced by the upheaval, folding, and faulting of sedimentary and other rocks, and also mountains due to volcanic eruptions, and still others produced by igneous intrusions, and an endless array of secondary features resulting from erosion or earth sculpture. One of the most conspicuous features of the chain, and one which has been used as a basis for dividing it into two portions, is the presence in Wyoming of a broad plateau trending east and west, known as the Laramie Plains. This plateau, with a general elevation of about 7000 feet, reaches from the Grand Plateau in the east nearly to the Great Basin in the west and separates the northern from the southern Rockies. This great ‘pass’ was chosen for the route of the Union Pacific Railroad, the first of the several transcontinental railroads now in operation. The several ranges composing the southern Rockies are for the most part arranged with their larger axes in a generally north and south direction, while the trend of the northern Rockies, as well as of their component ranges, is in general northwest and southeast.
Within the United States the portion of the Rocky Mountains to the north of the Laramie Plains has been termed the Stony Mountains, a revival of the name applied to them by Lewis and Clark, during their historic explorations in 1804-06; and the portion of the southern Rockies, situated principally in Colorado, northern New Mexico, eastern Utah, etc., has been designated as the Park Mountains. These two systems of ranges are the best known portions of the chain of which they form a part, and together with the southern portion of the Canadian Rockies must of necessity be taken as representative of its entire extent.
The Stony Mountains contain among their leading topographic features many important mountain ranges. In Wyoming the representative uplifts are: The Big Horn range, which, extending from near the centre of the State about 150 miles northward, ends in Montana. It is due principally to a single great upward fold in the rocks; the east slope is precipitous and the west slope gently inclined. The crest line has an elevation of from 8000 to 13,000 feet, and Cloud Peak, the culminating point, rises 13,165 feet above the sea. The Wind River range, in the west-central part of the State, presents a fine series of rugged peaks along its crest, at least a dozen of which have elevations in excess of 11,000 feet, the highest being Fremont Peak, 13,700 feet. The Teton range, near the northwest border of the State, is the boldest and probably the finest of the series, and culminates in the Grand Teton, a spine-like peak, rising 13,691 feet above the sea and 7000 feet above Jackson Lake, from which it may be seen to the greatest advantage. The Wind River, Teton, and other neighboring ranges, situated principally in northwest Wyoming, rise from a region some 15,000 square miles in area, which has a general elevation in excess of 8000 feet and is only exceeded in extent among the regions of similar elevation in North America by the central part of the Park Mountains. From
this mountainous plateau of Wyoming, and supplied principally by the melting of the snow on the lofty ranges, the Yellowstone River flows eastward to join the Missouri, and the Snake River flows westward and unites with the Columbia: the many head-branches of these two important waterways adjoin along the continental divide. In central Idaho there is a great region of sharp, serrate peaks, the character of which is expressed by the name of the main or Sawtooth range, by estimate about 13,000 feet high. Topographically this rugged region extends northwest and is known in part as the Bitter Root and the Cœur d'Alêne Mountains, which, although not remarkable for their height, are of great extent and important on account of their mines, forests, and fine scenery. In Montana there are also several distinct and important ranges, among which there are not less than 23 peaks that exceed 10,000 feet in height above the sea and rise from 6000 to 8000 feet above the neighboring valleys.
To the east of the Big Horn Mountains and separated from them by a portion of the Great Plateaus, 150 miles wide, are the Black Hills, which in a general view are included in the Rocky Mountains. These hills are due to a dome-like elevation of the generally horizontal rocks underlying the Great Plateaus, measuring about 80 by 160 miles, which if uneroded would have a height of some 7000 feet above the surrounding plain. Erosion has cut deeply into the uplift, however, and produced a rugged topography, especially in its central part, where granitic rocks are exposed. The culminating summit, Harney Peak, has an elevation of 7216 feet and rises about 2700 feet above the surrounding plain.
The Park Mountains, situated to the south of the Wyoming Plateau, are composed of many distinct ranges having a north and south trend, to which, however, a marked exception is furnished by the Uintah range in southwest Wyoming and northeast Utah, which consists of a deeply dissected east and west fold or broadly uplifted plateau. Intervening between several of the adjacent ranges, especially in Colorado, there are wide, nearly flat-bottomed valleys which owe their leading characteristics to the depth of the deposits of debris swept into them from the bordering uplands by streams and the wind. These valleys are known as ‘parks’ and suggested the name for the mountain system in which they occur. Typical examples are furnished by North, Middle, South, and San Luis parks in central Colorado, the broad generally level floors of which have elevations ranging from 7000 to 8000 feet.
Among the numerous ranges of the Park Mountains in Colorado are the Front or Colorado range, in view from Denver, the Saguache, Elk, San Juan ranges, etc. A conspicuous feature in the relief is the generally great elevation and the large number of lofty summits. The area above an elevation of 10,000 feet is much larger than any other region with a similar altitude in North America. Among the host of magnificent mountain peaks there are more than 30 which exceed 14,000 feet, but their height is seldom fully appreciated, owing to the elevation of the neighboring valleys, which reduces their visual height to about one-half of their total elevation above the sea. Of this multitude of magnificent individual mountains or peaks, as many of them are termed, the best known and perhaps most representative
are, with their elevations expressed in feet: Gray's Peak, 14,341; Mount Harvard, 14,325; Mountain of the Holy Cross, 14,000; Mount Lincoln, 14,297; Long's Peak, 14,271; Mount Princeton, 14,196; Pike's Peak, 14,108; Uncompahgre Peak, 14,289; and Mount Yale, 14,187, In the opinion of many observers the most magnificent mountain mass in the Park Mountains, largely on account of its isolation, is Sierra Blanca, in southeast Colorado, 14,465 feet.
The Park Mountains extend west into Utah and there include the bold Wasatch range, with a culminating summit nearly 12,000 feet above the sea. This range is in view from Ogden and Salt Lake City and presents a wonderfully bold escarpment to the west, which sharply defines the west border of the Rocky Mountains for a distance of some 200 miles.
To the southwest of the as yet indefinitely determined border of the Park Mountains is a series of high plateaus termed collectively the Colorado Plateaus, situated principally in Arizona, western New Mexico, and southern Utah, which have elevations ranging from 7000 to 8000 feet, and have been deeply dissected by the Colorado River and its tributaries. The explorations of J. S. Newberry, J. W. Powell, and C. E. Dutton in this land of remarkable cañons have made it one of the best known and to geologists and geographers most instructive portions of the Rocky Mountain region.
In New Mexico the mountains are lower than in Colorado, and the several ranges and numerous isolated volcanic mountains are separated by broad deeply filled valleys. These same characteristics of the relief extend southward into Mexico, where the Rocky Mountains terminate and are succeeded by a series of lofty volcanoes, and by the western portion of the Antillean Cordillera, in which the major structural features are folds and faults, trending east and west.
Geologically the Rocky Mountains present a wide range in reference especially to the age of the rocks and to the structure of the numerous ranges. All of the larger divisions of geological history from the Archæan to recent times are represented. Granite, gneiss, schist, and related rocks usually referred to the Archæan occur especially in the axial portion of many of the ranges, as the Front or Colorado range, the Saguache, etc., in Colorado, the Black Hills, Big Horn, Teton, etc. The older recognized sedimentary rocks belong to the Algonkian period and consist largely of quartzites. In the Lewis and Livingston of Montana rocks of this age have yielded interesting remains of large crustaceans related to Eurypterus, which belong to the oldest known fauna of the earth. In sandstone of Ordovician (Lower Silurian) age near Cañon City, Colo., the oldest known fossil fishes have been found. Carboniferous rocks, principally marine limestone, occur widely throughout both the Stony and Park Mountains. At several localities in Colorado and Wyoming rocks of Jura-Trias age have yielded large quantities of bones belonging to gigantic extinct reptiles. Marine sediments of Cretaceous age, particularly in Montana, are frequently crowded with beautifully preserved shells, and particularly a great variety of cephalopods. Tertiary rocks, consisting principally of the sediments of lakes and occurring for the most part in the valley, contain the bones of many genera of extinct mammals, some of
them of large size and remarkable character. In beds of similar age, consisting largely of volcanic dust, at Florissant, Colo., immense numbers of fossil insects have been obtained, and near Green River in Wyoming soft shales are crowded with the remains of fishes. Fossil plants, particularly of Lower Cretaceous, Jurassic, and Tertiary times, are also abundant. Valuable coal seams of Cretaceous and Tertiary age occur at many localities.
One of the most remarkable facts concerning the geological structure of the Rocky Mountains is the presence of a series of abrupt folds along their eastern border in which the horizontal strata, several thousand feet thick, underlying the Great Plateaus, are bent upward. Remnants of these same beds spared by erosion occur in several of the ranges to the west of the Front range, at an elevation of 5000 or 6000 feet above the portions not affected by mountain-building forces. At many localities along the east base of the Front range, from New Mexico northward far into Canada, the abrupt folding of the rocks is shown by the nearly vertical position of the eroded border of the strata remaining. At times the folds were overturned eastward, so that the beds in their eroded basal portions dip westward. In northern Montana a still more intense movement resulted in the fracturing of the rocks in an overturned fold, producing a nearly horizontal fault or thrust plain, in connection with which, as reported by Bailey Willis, Algonkian rocks were carried seven miles eastward and rest on Cretaceous strata.
In general the various ranges composing the Rocky Mountain chain are due to upward folds or anticlinals in sedimentary and igneous rocks, and the elevation of plastic magmas now represented by granite, gneiss, schist, etc., in their central portions. In general, also, as shown by the north and south trend of the longer axes of the folds, the direction in which the force acted which caused the rocks to bend was east and west. The principal movements which upraised the mountains occurred at the close of the Mesozoic, as is shown by unconformities between Mesozoic and Tertiary beds.
The upheaval of the mountains was followed by erosion. Nearly all of the scenic features which now attract the eye are due to the work of streams and glaciers which have deeply sculptured the upheaved mountain blocks. The broad valleys, including the parks of Colorado, etc., are due to the upraising of their bordering mountains; but the cañons, such as the Yellowstone, Arkansas, Colorado, and other streams flow through, are the result of abrasion by the debris-charged rivers themselves. The infinitely varied secondary valleys and cañons and the multitude of gorges, gulches, amphitheatres, and other similar incised features of the relief are due to erosion, while the countless mesas, buttes, pinnacles, etc., which rise above the general level of the surrounding country are remnants of ancient uplands spared by the erosive agencies. Erosion or earth sculpture has also brought out the characteristic features of the Black Hills in which the more resistant rocks stand in relief and the weaker beds underlie valleys, and has given to the several regions of ‘bad lands’ their unique topography. In addition to the numerous ranges due to lateral pressure and consequent upward folding there are many elevations due to volcanic
agencies. Mountains built by volcanic eruptions are numerous in Arizona and New Mexico. To this class belong San Francisco Mountain and Mount Taylor, situated farther east, in sight of which there are a large number of ‘volcanic necks’ exposed by the removal of the craters which once inclosed them. East of the Front range in New Mexico, and well out in the Great Plateaus, there are a number of conspicuous volcanic craters, of which the leading example is Mount Capulin, 2750 feet high above the surrounding plain, and with a crater on its summit nearly a mile in diameter. The Spanish Peaks, in southeastern Colorado, furnish admirable examples of the deep erosion of large volcanic mountains. Colorado, Wyoming, and Montana are almost wholly without recent volcanic craters, but in Western Wyoming and extending across southern Idaho are the basaltic lavas of the Snake River Plains, one of the most wonderful exhibits of its kind in the world, associated with which there are numerous volcanic craters. In the region of Yellowstone Park there are great accumulations of rhyolitic lava, of older date than the basalts of Idaho, but still retaining some of their volcanic heat, as is made manifest by the numerous hot springs and geysers. Associated with volcanic eruptions is the injection from below of molten or plastic magmas into the rigid rocks composing the outer portion or ‘crust’ of the earth. These intrusions in part occupy fissures and form dikes, but at times were forced between stratified beds and produced intruded sheets of igneous rocks, perhaps many scores of square miles in area, and under other conditions formed cistern-like intrusions termed laccoliths, which raised the rocks above into domes. In the Rocky Mountains there are numerous examples of each of these varieties of igneous intrusions, many of which have been laid bare by erosion. Of these the most remarkable are the laccoliths forming the Henry Mountains in southern Utah, where several intrusions in previously horizontal rocks elevated domes measuring three to five miles in diameter and from a few hundred to fully 7000 feet high. These mountains furnished the type of a class of uplifts not previously recognized. Other similar laccolithic mountains occur in southwest Colorado, and about the Black Hills in South Dakota, and have been recognized elsewhere.
Perennial snow banks and miniature glaciers occur in the mountains of Colorado and on the Teton range in Wyoming. In northern Montana small glaciers are frequent, and in the Canadian Rockies form a conspicuous feature in the magnificent scenery. The best known is perhaps Illicilliwaet glacier, near Glacier House, on the line of the Canadian Pacific Railroad. Other glaciers occur in the higher portions of the mountains throughout Alberta. The glaciers are all of the Alpine type, and from Montana northward are remnants of great ice sheets which covered the mountains during the Glacial epoch. Many of the more conspicuous features in the North Rockies, such as the deep, steep-sided valley, with rounded or U-shaped bottoms, numerous lakes and side alcoves from which the streams descend in cascades, are due to the former glaciers which flowed away from the several ranges. The summit portions of the Big Horn, Teton, and other ranges in Wyoming are glaciated, as is also a large area in the region of great mountains in Colorado. Nearly all of the numerous and
frequently exceedingly beautiful lakes of the Rocky Mountain region are due to the work of glacial ice. Those near the crests of the higher ranges are, for the most part, rock-basins, while those at lower altitudes, and especially the long, narrow lakes in the larger valleys, are held by morainal dams.
The chief industry throughout the Rocky Mountains from Alaska to Mexico is mining, and silver, gold, copper, and coal are the leading products. Next in importance is stock-raising, and particularly cattle-raising, for which the nutritious bunch grass, growing mostly below the lower limit of the forests, furnishes abundant nourishment. In recent years, however, overgrazing has greatly injured the natural pasture lands south of Montana. Agriculture is of local importance, and with certain exceptions, mostly in western Idaho and adjacent portions of Washington, is dependent on irrigation. All through the region from the central part of British Columbia to Central Mexico there are ranches, mining camps, villages, and cities. At present seven railroads, six in the United States and one in Canada, cross the chain, and another to the north of the Canadian Pacific Railroad is projected. In Mexico the main avenues of traffic run north and south through the intermontane valleys, as is shown by the Mexican Central Railway, which connects Ciudad Juarez, opposite El Paso, Texas, with the City of Mexico, a distance of over 1000 miles. These several railroads and their numerous branches make accessible nearly all portions of the Rocky Mountain region, except the extreme north and the excessively rugged western portion of the tableland of Mexico. At the far north, however, a new centre of industry has developed in the Klondike region. The forests of the mountains are economically important, not only as a source of lumber, but also because they serve to regulate the flow of streams used for irrigation. For these reasons 21 forest reserves, with a total area of over 38,000 square miles, have been established in the portion of the Rocky Mountains belonging to the United States, and similar provisions have been made in Canada.
Among the economic assets of the Rocky Mountains should also be included their magnificent scenery and healthful and invigorating climate. Although thousands of people visit them each year in search of health and recreation, the great benefits to be reaped in these directions are as yet only partially appreciated. The portions most attractive to travelers are the Yellowstone National Park and the Grand Cañon of the Colorado, each of which is unrivaled in its class.
Flora. The Rocky Mountains constitute one of the great floral regions of North America. With the exception of southern New Mexico and Arizona, which belong botanically to the Mexican Plateau, and the extreme northern portion, whose flora is still but little known and merges with that of the Pacific Coast, the flora of the whole Rocky Mountain region is essentially homogeneous at corresponding altitudes. On the other hand, the region is markedly different from the Eastern or Appalachian region. Scarcely 20 per cent. of the Rocky Mountain plants are found in the East, and of these most belong to the species common to both hemispheres. The Rocky Mountain flora, however, includes numerous species found in the contiguous regions, and is especially
allied to that of the California or Sierra Nevada region. Within certain altitudes forests occur throughout the Rocky Mountain region. The upper limit of tree growth, or cold timber line, rises toward the south, having an elevation of 9000 feet on the international boundary and 11,000 to 12,000 feet in Colorado. In the Stony and Park Mountains and thence southward there is also a lower limit of tree growth, determined mainly by lack of humidity. As far north as Idaho and southern Wyoming the larger valleys are below this dry timber line, but in Canada the forests are continuous across mountain and valley. The forests of the whole region are overwhelmingly coniferous, and with the exception of two alpine junipers none of the coniferous trees are common to the Appalachian region, though the latter has closely allied corresponding species, some of which have been erroneously identified with those of the Rockies. There are about 10 pines, and the most characteristic tree of the whole region is the Western yellow pine (Pinus ponderosa). The nut pine (Pinus edulis) and the Pinus Chihuahua are the chief species confined to the southern portion, while the mountain pine (Pinus monticola) and the black pine (Pinus Murrayana) are found chiefly in the north. Of the spruces the Picca Engelmanni is the most common throughout the region, though generally seeking higher altitudes (nearly 9000 feet in the south). Other spruces, notably the Picea Columbiana, are more common in the north, and a northern habitat is also preferred by the firs (Abies grandis and nobilis), the Western Hemlock (Tsuga Mertensiana), and the tamarack (Larix Americana). Shrubby conifers, such as junipers, are found chiefly in the arid southwestern ranges and above the timber line. The deciduous forests of the Rocky Mountains are of small extent and poor in species. There are six species of oak, but all rather small and scrubby, and the other deciduous tree families are similarly ill represented. Sycamores, the New Mexican locust, and mulberries grow in the south, and the rivers throughout the region are lined with cottonwood, balsam poplar, and willows. On the level plateaus the predominating flora is of the sage-brush type, represented by the genera Artemisia, Atriplex, Eurotina, and Bigelovia, but in the southwest the plains are nearly desert, with the characteristic desert flora. Above the timber line the Alpine flora closely resembles the flora of the Arctic region. Among all the flowering plants of the Rocky Mountains the families best represented are in the order named, the Compositæ, Gramineæ, Papilionaceæ, Cyperaceæ, Ranunculaceæ, Cichoriaceæ, Polygonaceæ, Onagraceæ, and Umbelliferæ. Of these the first two together include about 25 per cent. of all the species.
Fauna. It was the opinion of the earlier students of animal life in North America that the Rocky Mountains were the central and essential part of a peculiar fauna representing the ‘Central’ zoögeographical region embracing the whole elevated territory between the Great Plains and the base of the Sierra Nevada. It appears, however, that such a distinction does not exist; that the Rocky Mountains are peculiar only in such features as depend upon altitude and are correlated with climate and vegetation as locally determined by height above the sea and consequent low temperature. The fauna of all North
America is remarkably diffuse and uniform, so that it is considered indivisible by any well-marked distinctions; nevertheless certain zones of life roughly bounded by summer isothermal lines have been recognized as Boreal, Hudsonian, Canadian, Alleghanian, Carolinian, etc., in succession from north to south. These are reproduced in the Rocky and other high ranges of the West. The height above the general base-level at which such life-zones will be found depends upon the latitude. Thus at the northern extremity of the range, near the mouth of the Mackenzie, not only the summits but the base of the range are within the ‘Boreal zone;’ but at the southern extremity in New Mexico, the base exhibits a Carolinian or even warmer type of fauna, and one must climb 13,000 or 14,000 feet to find upon the peaks Arctic weather, and Arctic plants and animals. It is in these restricted summit areas that one finds the animals peculiar to the region; in the valleys and parks there is little that is distinctive. It is only when one has risen considerably that local specialties begin to appear. Thus in a medium latitude (say Montana) at about 9000 feet, one rises above the sagebrush, the Douglas fir, and the black pine, with their host of valley and plain animals, and into forests of Alpine fir, white-bark and Engelmann's pines, which indicate a climate equivalent to that about Hudson Bay. Here are breeding snow-birds (Junco), the nut-cracker, Canada jay, kinglet, and other northerly birds. This zone extends to the timber line and forms the normal upward limit of the wapiti, moose, and mule deer; the grizzly and black bears; the wolverine, many mice, squirrels, and the smaller carnivores that prey upon them. At and near the timber line one begins to find among the stunted trees and plants animals which do not come lower down, but spend their lives altogether there and upon the treeless summits above it, and these are the really characteristic mountain animals; and yet with very few exceptions (the sewellel is most conspicuous) they are the same as those of subarctic America generally or of the high ranges of the Pacific Coast, or different only in specific details. Such among the larger animals are the bighorn, and the Rocky Mountain white goat (qq.v.). The former is practically a circumpolar form, and the latter is numerous at sea-level in the far north, but is scarce in the United States. The bighorn is still to be found as far south as San Francisco Peak in Arizona. Along with these two game animals are several small ones peculiar to the heights. One of the most characteristic is the pika (Lagomys princeps); another is the lemming mouse (Phenacomys orophilus), an Arctic form that burrows in the moss of the Alpine meadows; and a third the whistler, a marmot (Arctomys), inhabiting these heights only toward the north. This, with a weasel, which descends in winter, when the small animals are hibernating or living upon their stores in underground burrows, and when the sheep have migrated below the snow line in order to find browse and pasturage, constitutes the list of peculiarly Rocky Mountain mammals. On the heights, however, breed certain birds, as species of ptarmigan, the rosy finches (Leucosticte), and an occasional golden eagle or great owl.
The general list of animals of the lower levels of the Rocky Mountain region is a very long one,
and includes many which are distinguished as local or geographic races or subspecies of more widely distributed forms. The bison, pronghorn, and the white-tailed deer range throughout the valleys and climb the heights to a considerable altitude in summer, and in the north caribou are common; but the bison is extinct, the wapiti remains only from northwestern Wyoming northward, and the pronghorn is scarce. Among the carnivores, grizzly and black bears, the puma, wildcat, wolverine, otter, marten, fisher, long-tailed weasel, black-footed ferret, badger, striped and spotted skunks, red fox, kit fox, raccoon, and cacomixl make a long list attractive in early days to trappers. An extensive catalogue of rodents includes a large number of local species of mice, wood-rats and voles, the beaver (now greatly reduced), muskrat, and several hares, one or two of which are peculiar; and many species or races of burrowing ‘gophers,’ and of arboreal and terrestrial squirrels. The same principles apply to the birds, of which about 400 species and varieties have been recorded as occurring in the central Rocky Mountain region, of which about 250 are known to breed there. A goodly list of reptiles and batrachians and fishes may be compiled, the last group distinguished by the predominance of salmonoids. Several species of the Pacific coast salmon regularly reach the Rocky Mountains by ascending the Columbia, Fraser, and more northerly rivers. Insects abound and this region is the headquarters of the locust tribe in America.
In general it may be said that what is most peculiar in the fauna of the Rocky Mountain region has been derived from the north, and leads back to the Glacial period, when the preglacial boreal fauna was pressed southward by the slow cooling and final refrigeration of Canada. When the ice slowly melted under the restoration of warmer conditions a large representation of this Arctic fauna found upon the summits a local continuance of the cool climate favorable to it, and has remained there, often in the south isolated upon peaks which it cannot leave, and where it has survived in limited colonies cut off from the north. This history (which was also that of the Coast ranges) and the barriers afforded by the breadth of high, dry plains to the eastward, account for the greater likeness of the Rocky Mountain fauna on the whole to the Pacific than to the Atlantic side of the continent.
Bibliography. United States Geographical and Geological Survey of the Rocky Mountains (Washington, 1868 et seq.); McClure, Three Thousand Miles Through the Rocky Mountains (Philadelphia, 1869); Farmer, The Resources of the Rocky Mountains, Mineral, Grazing, Agricultural, and Timber (Cleveland, 1883); Ingersoll, The Crest of the Continent (Chicago, 1885); Coulter, Manual of the Botany of the Rocky Mountain Region (New York, 1885); Parkman, The Oregon Trail (ib., 1880); Shaler, Nature and Man in America (ib., 1892); Sivers, America (Leipzig, 1894).