Physiography.—Colorado embraces in its area a great variety of plains, mountains and plateaus. It lies at the junction of the Great Plains—which in their upward slant to the westward attain an average elevation of about 4000 ft. along the east boundary of the state—with the Rocky Mountains, to the west of which is a portion of the Colorado Plateau. These are the three physiographic provinces of the state (see also [United States], section Geology, ad fin., for details of structure). The last-named includes a number of lofty plateaus—the Roan or Book, Uncompahgre, &c., which form the eastern continuation of the high plateaus of Utah—and covers the western quarter of the state. Its eastern third consists of rich, unbroken plains. On their west edge lies an abrupt, massive, and strangely uniform chain of mountains, known in the neighbourhood of Colorado Springs as the Rampart Range, and in the extreme north as the Front Range, and often denominated as a whole by the latter name. The upturning of the rocks of the Great Plains at the foot of the Front Range develops an interesting type of topography, the harder layers weathering into grotesquely curious forms, as seen in the famous Garden of the Gods at the foot of Pike’s Peak. Behind this barrier the whole country is elevated 2000 ft. or so above the level of the plains region. In its lowest portions just behind the front ranges are the natural “parks”—great plateaus basined by superb enclosing ranges; and to the west of these, and between them, and covering the remainder of the state east of the plateau region, is an entanglement of mountains, tier above tier, running from north to south, buttressed laterally with splendid spurs, dominated by scores of magnificent peaks, cut by river valleys, and divided by mesas and plateaus. These various chains are known by a multitude of local names. Among the finest of the chains are the Rampart, Sangre de Cristo, San Juan, Sawatch (Saguache) and Elk ranges. The first, like the other ranges abutting from north to south upon the region of the prairie, rises abruptly from the plain and has a fine, bold outline. It contains a number of fine summits dominated by Pike’s Peak (14,108 ft.). Much more beautiful as a whole is the Sangre de Cristo range. At its southern end are Blanca Peak (14,390) and Old Baldy (14,176, Hayden), both in Costilla county; to the northward are Rito Alto Peak (12,989, Wheeler), in Custer county, and many others of almost equal height and equal beauty. The mountains of the south-west are particularly abrupt and jagged. Sultan Mountain (13,366, Hayden), in San Juan county, and Mt. Eolus (14,079), in La Plata county, dominate the fine masses of the San Juan ranges; and Mt. Sneffels (14,158, Hayden), Ouray county, and Uncompahgre Peak (14,289), Hinsdale county, the San Miguel and Uncompahgre ranges, which are actually parts of the San Juan. Most magnificent of all the mountains of Colorado, however, are the Sawatch and adjoining ranges in the centre of the state. The former (the name is used a little loosely) consists of almost a solid mass of granite, has an average elevation of probably 13,000 ft., presents a broad and massive outline, and has a mean breadth of 15 to 20 m. Mt. Ouray (13,956 ft.), in Chaffee county, may be taken as the southern end, and in Eagle county, the splendid Mount of the Holy Cross (14,170)—so named from the figure of its snow-filled ravines—as the northern. Between them lie: in Chaffee county, Mt. Shavano (14,239, Hayden), Mt. Princeton (14,196, Hayden), Mt. Yale (14,187, Hayden), Mt. Harvard (14,375, Hayden), and La Plata Peak (14,342); in Pitkin county, Grizzly Peak (13,956, Hayden); in Lake county, Elbert Peak (14,421), and Massive mountain (14,424), the highest peak in the state; on the boundary between Summit and Park counties, Mt. Lincoln (14,297, Hayden); and, in Summit county, Mt. Fletcher (14,265). The Elk range is geologically interesting for the almost unexampled displacement of the strata of which it is composed, and the apparent confusion which has thence arisen. Among the most remarkable of its separate summits, which rise superbly in a crescent about Aspen, are North Italian Peak (13,225), displaying the red, white and green of Italy’s national colours, White Rock Mountain (13,532), Mt. Owen (13,102), Teocalli Mountain (13,220), Snow Mass (13,970, Hayden) and Maroon (14,003, Hayden) mountains, Castle Peak (14,259), Capitol Mountain (13,997, Hayden), Pyramid Peak (13,885, Hayden), Taylor Peak (13,419), and about a dozen other summits above 12,000 ft. A few miles to the north and north-east of the Mount of the Holy Cross are Red Mountain (13,333, Wheeler), in Eagle county, Torrey Peak (14,336, Hayden) and Gray’s Peak (14,341, Hayden), in Summit county, Mt. Evans (14,330, Hayden), in Clear Creek county, and Rosalie Peak (13,575), in Park county; a little farther north, in Gilpin, Grand and Clear Creek counties, James Peak (13,283, Hayden), and, in Boulder county, Long’s Peak (14,271, Hayden). Many fine mountains are scattered in the lesser ranges of the state. Altogether there are at least 180 summits exceeding 12,000 ft. in altitude, more than 110 above 13,000 and about 40 above 14,000.
Cirques, valley troughs, numberless beautiful cascades, sharpened alpine peaks and ridges, glacial lakes, and valley moraines offer everywhere abundant evidence of glacial action, which has modified profoundly practically all the ranges. The Park Range east of Leadville, and the Sawatch Range, are particularly fine examples. Much of the grandest scenery is due to glaciation.
One of the most remarkable orographical features of the state are the great mountain “parks”—North, Estes, Middle, South and San Luis—extending from the northern to the southern border of the state, and lying (with the exception of Middle Park) just east of the continental divide. These “parks” are great plateaus, not all of them level, lying below the barriers of surrounding mountain chains. North Park, the highest of all, is a lovely country of meadow and forest. Middle Park is not level, but is traversed thickly by low ranges like the Alleghanies; in the bordering mountain rim are several of the grandest mountain peaks and some of the most magnificent scenery of the state. Estes Park is small, only 20 m. long and never more than 2 m. broad; it is in fact the valley of Thompson Creek. Its surface is one of charming slopes, and by many it is accounted among the loveliest of Colorado valleys. Seven ranges lie between it and the plains. South Park is similarly quiet and charming in character. Much greater than any of these is San Luis Park. The surface is nearly as flat as a lake, and it was probably at one time the bed of an inland sea. In the centre there is a long narrow lake fed by many streams. It has no visible outlet, but is fresh. The San Luis Park, which runs into New Mexico, is traversed by the Rio Grande del Norte and more than a dozen of its mountain tributaries. These parks are frequented by great quantities of large game, and—especially the North and Middle—are famous hunting-grounds. They are fertile, too, and as their combined area is something like 13,000 sq. m. they are certain to be of great importance in Colorado’s agricultural development.
The drainage system of the state is naturally very complicated. Eleven topographical and climatic divisions are recognized by the United States Weather Bureau within its borders, including the several parks, the continental divide, and various river valleys. Of the rivers, the North Platte has its sources in North Park, the Colorado (the Gunnison and Grand branches) in Middle Park, the Arkansas and South Platte in South Park—where their waters drain in opposite directions from Palmer’s Lake—the Rio Grande in San Luis Park. Three of these flow east and south-east to the Missouri, Mississippi and the Gulf; but the waters of the Colorado system flow to the south-west into the Gulf of California. Among the other streams, almost countless in number among the mountains, the systems of the Dolores, White and Yampa, all in the west, are of primary importance. The scenery on the head-waters of the White and Bear, the upper tributaries of the Gunnison, and on many of the minor rivers of the south-west is wonderfully beautiful. The South Platte falls 4830 ft. in the 139 m. above Denver; the Grand 3600 ft. in the 224 m. between the mouth of the Gunnison and the Forks; the Gunnison 6477 ft. in 200 m. to its mouth (and save for 16 m. never with a gradient of less than 10 ft.); the Arkansas 7000 ft. in its 338 m. west of the Kansas line. Of the smaller streams the Uncompahgre falls 2700 ft. in 134 m., the Las Animas 7190 ft. in 113 m., the Los Pinos 4920 ft. in 75 m., the Roaring Fork 5923 ft. in 64 m., the Mancos 5000 ft. in 62 m., the La Plata 3103 ft. in 43 m., the Eagle 4293 ft. in 62 m., the San Juan 3785 in 303, the Lake Fork of the Gunnison 6047 in 59. The canyons formed in the mountains by these streams are among the glories of Colorado and of America. The grandest are the Toltec Gorge near the Southern boundary line, traversed by the railway 1500 ft. above the bottom; the Red Gorge and Rouge Canyon of the Upper Grand, and a splendid gorge 16 m. long below the mouth of the Eagle, with walls 2000-2500 ft. in height; the Grand Canyon of the Arkansas (8 m.) above Canyon City, with granite walls towering 2600 ft. above the boiling river at the Royal Gorge; and the superb Black Canyon (15 m.) of the Gunnison and the Cimarron. But there are scores of others which, though less grand, are hardly less beautiful. The exquisite colour contrasts of the Cheyenne canyons near Colorado Springs, Boulder Canyon near the city of the same name, Red Cliff and Eagle River Canyons near Red Cliff, Clear Creek Canyon near Denver—with walls at places 1000 ft. in height—the Granite Canyon (11 m.) of the South Platte west of Florissant, and the fine gorge of the Rio de las Animas (1500 ft.), would be considered wonderful in any state less rich in still more marvellous scenery. One peculiar feature of the mountain landscapes are the mines. In districts like that of Cripple Creek their enormous ore “dumps” dot the mountain flanks like scores of vast ant-hills; and in Eagle River canyon their mouths, like dormer windows into the granite mountain roof, may be seen 2000 ft. above the railway.
Many parts of the railways among the mountains are remarkable for altitude, construction or scenery. More than a dozen mountain passes lie above 10,000 ft. Argentine Pass (13,000 ft.), near Gray’s Peak, is one of the highest wagon roads of the world; just east of Silverton is Rio Grande Pass, about 12,400 ft. above sea-level, and in the Elk Mountains between Gunnison and Pitkin counties is Pearl Pass (12,715 ft.). Many passes are traversed by the railways, especially the splendid scenic route of the Denver and Rio Grande. Among the higher passes are Hoosier Pass (10,309 ft.) in the Park Range, and Hayden Divide (10,780) and Veta Pass (9390); both of these across the Sangre de Cristo range; the crossing of the San Miguel chain at Lizard Head Pass (10,250) near Rico; of the Uncompahgre at Dallas Divide (8977) near Ouray; of the Elk and Sawatch ranges at Fremont (11,320), Tennessee (10,229), and Breckenridge (11,470) passes, and the Busk Tunnel, all near Leadville; and Marshall Pass (10,846) above Salida. Perhaps finer than these for their wide-horizoned outlooks and grand surroundings are the Alpine Tunnel under the continental divide of the Lower Sawatch chain, the scenery of the tortuous line along the southern boundary in the Conejos and San Juan mountains, which are crossed at Cumbres (10,003 ft.), and the magnificent scenery about Ouray and on the Silverton railway over the shoulder of Red Mountain (attaining 11,235 ft.). Notable, too, is the road in Clear Creek Canyon—where the railway track coils six times upon itself above Georgetown at an altitude of 10,000 ft.
Climate.—The climate of Colorado is exceptional for regularity and salubrity. The mean annual temperature for the state is about 46°. The mean yearly isothermals crossing the state are ordinarily 35° to 50° or 55° F. Their course, owing to the complex orography of the state, is necessarily extremely irregular, and few climatic generalizations can be made. It can be said, however, that the south-east is the warmest portion of the state, lying as it does without the mountains; that the north-central region is usually coldest; that the normal yearly rainfall for the entire state is about 15.5 in., with great local variations (rarely above 27 in.). Winds are constant and rather high (5 to 10 m.), and for many persons are the most trying feature of the climate. Very intense cold prevails of course in winter in the mountains, and intense heat (110° F. or more in the shade) is often experienced in summer, temperatures above 90° being very common. The locality of least annual thermometric range is Lake Moraine (10,268 ft. above the sea)—normally 91° F.; at other localities the range may be as great as 140°, and for the whole state of course even greater (155° or slightly more). The lowest monthly mean in 16 years (1887-1903) was 17.30. Nevertheless, the climate of Colorado is not to be judged severe, and that of the plains region is in many ways ideal. In the lowlands the snow is always slight and it disappears almost immediately, even in the very foothills of the mountains, as at Denver or Colorado Springs. However hot the summer day, its night is always cool and dewless. Between July and October there is little rain, day after day bringing a bright and cloudless sky. Humidity is moderate (annual averages for Grand Junction, Pueblo, Denver and Cheyenne, Wyo., for 6 A.M. about 50 to 66; for 6 P.M. 33 to 50); it is supposed to be increasing with the increasing settlement of the country. Sunshine is almost continuous, and splendidly intense. The maximum number of “rainy” days (with a rainfall of more than 0.01 in.) rarely approaches 100 at the most unfortunate locality; for the whole state the average of perfectly “clear” days is normally above 50%, of “partly cloudy” above 30, of “cloudy” under 20, of “rainy” still less. At Denver, through 11 years, the actual sunlight was 70% of the possible; many other points are even more favoured; very many enjoy on a third to a half of the days of the year above 90% of possible sunshine. All through the year the atmosphere is so dry and light that meat can be preserved by the simplest process of desiccation. “An air more delicious to breathe,” wrote Bayard Taylor, “cannot anywhere be found; it is neither too sedative nor too exciting, but has that pure, sweet, flexible quality which seems to support all one’s happiest and healthiest moods.” For asthmatic and consumptive troubles its restorative influence is indisputable. Along with New Mexico and Arizona, Colorado has become more and more a sanitarium for the other portions of the Union. Among the secondary hygienic advantages are the numerous mineral wells.
Flora and Fauna.—The life zones of Colorado are simple in arrangement. The boreal embraces the highest mountain altitudes; the transition belts it on both sides of the continental divide; the upper Sonoran takes in about the eastern half of the plains region east of the mountains, and is represented further by two small valley penetrations from Utah. Timber is confined almost wholly to the high mountain sides, the mountain valleys and the parks being for the most part bare. Nowhere is the timber large or dense. The timber-line on the mountains is at about 10,000 ft., and the snow line at about 11,000. It is supposed that the forests were much richer before the settlement of the state, which was followed by reckless consumption and waste, and the more terrible ravages of fire. In 1872-1876 the wooded area was estimated at 32% of the state’s area. It is certainly much less now. The principal trees, after the yellow and lodgepole pines, are the red-fir, so-called hemlock and cedar, the Engelmann spruce, the cottonwood and the aspen (Populus tremuloides). In 1899 Federal forest reserves had been created, aggregating 4849 sq. m. in extent, and by 1910 this had been increased to 24,528 sq. m. The reserves cover altitudes of 7000 to 14,000 ft. The rainfall is ample for their needs, but no other reserves in the country showed in 1900 such waste by fire and pillage. The minor flora of the country is exceedingly rich. In the plains the abundance of flowers, from spring to autumn, is amazing.
Large game is still very abundant west of the continental divide. The great parks are a favourite range and shelter. Deer and elk frequent especially the mountains of the north-west, in Routt and Rio Blanco counties, adjoining the reservations of the Uncompahgre (White River Ute) and Uintah-Ute Indians—from whose depredations, owing to the negligence of Federal officials, the game of the state has suffered enormous losses. The bison have been exterminated. Considerable bands of antelope live in the parks and even descend to the eastern plains, and the mule-deer, the most common of large game, is abundant all through the mountains of the west. Grizzly or silver-tip, brown and black bears are also abundant in the same region. Rarest of all is the magnificent mountain sheep. Game is protected zealously, if not successfully, by the state, and it was officially estimated in 1898 that there were then probably 7000 elk, as many mountain sheep, 25,000 antelope and 100,000 deer within its borders (by far the greatest part in Routt and Rio Blanco counties). Fish are not naturally very abundant, but the mountain brooks are the finest home for trout, and these as well as bass, cat-fish and some other varieties have been used to stock the streams.
Soil.—The soils of the lowlands are prevailing sandy loams, with a covering of rich mould. The acreage of improved lands in 1900 was returned by the federal census as 2,273,968, three times as much being unimproved; the land improved constituted 3.4% of the state’s area. The lands available for agriculture are the lowlands and the mountain parks and valleys.
Speaking generally, irrigation is essential to successful cultivation, but wherever irrigation is practicable the soil proves richly productive. Irrigation ditches having been exempted from taxation in 1872, extensive systems of canals were soon developed, especially after 1880. The Constitution of Colorado declares the waters of its streams the property of the state, and a great body of irrigation law and practice has grown up about this provision. The riparian doctrine does not obtain in Colorado. In no part of the semi-arid region of the country are the irrigation problems so diverse and difficult. In 1903 there were, according to the governor, 10 canals more than 50 m. in length, 51 longer than 20 m., and hundreds of reservoirs. In 1899 there were 7374 m. of main ditches. The average annual cost of water per acre was then estimated at about 79 cents. The acres under ditch in 1902 were greater (1,754,761) than in any other state; and the construction cost of the system was then $14,769,561 (an increase of 25.6% from 1899 to 1902). There are irrigated lands in every county. Their area increased 8.9% in 1899-1902, and 80.9% from 1890 to 1900; in the latter year they constituted 70.9% of the improved farm-land of the state, as against 48.8 in 1890. The land added to the irrigated area in the decade was in 1890 largely worthless public domain; its value in 1900 was about $29,000,000. As a result of irrigation the Platte is often dry in eastern Colorado in the summer, and the Arkansas shrinks so below Pueblo that little water reaches Kansas. The water is almost wholly taken from the rivers, but underflow is also utilized, especially in San Luis Park. The South Platte is much the most important irrigating stream. Its valley included 660,495 acres of irrigated land in 1902, no other valley having half so great an area. The diversion of the waters of the Arkansas led to the bringing of a suit against Colorado by Kansas in the United States Supreme Court in 1902, on the ground that such diversion seriously and illegally lessened the waters of the Arkansas in Kansas. In 1907 the Supreme Court of the United States declared that Colorado had diverted waters of the Arkansas, but, since it had not been shown that Kansas had suffered, the case was dismissed, without prejudice to Kansas, should it be injured in future by diversion of water from the river. The exhaustion, or alleged exhaustion, by irrigation in Colorado of the waters of the Rio Grande has raised international questions of much interest between Mexico and the United States, which were settled in 1907 by a convention pledging the United States to deliver 60,000 acre-feet of water annually in the bed of the Rio Grande at the Acequia Madre, just above Juarez, in case of drought this supply being diminished proportionately to the diminution in the United States. As a part of the plans of the national government for reclamation of land in the arid states, imposing schemes have been formulated for such work in Colorado, including a great reservoir on the Gunnison. One of the greatest undertakings of the national reclamation service is the construction of 77 m. of canal and of a six-mile tunnel, beneath a mountain, between the canyon of the Gunnison and the valley of the Uncompahgre, designed to make productive some 140,000 acres in the latter valley.