Physical Geography

Colorado lies in three major physical regions of the United States—the Great Plains, the Rocky Mountains, and the Colorado Plateau.

The Great Plains. Eastern Colorado is part of the Great Plains. This section is some 150 miles (240 km) wide and covers more than a third of the state. It consists mainly of level to rolling land that slopes gradually upward to the foot of the Rocky Mountains. Elevations vary from about 3,400 feet (1,040 m) along the state's eastern border to as much as 6,000 feet (1,830 m) at the edge of the Rockies. Near the mountains and throughout much of the south the terrain becomes rougher and more varied. The southern section is broken by numerous mesas, buttes, and gorges.

The Rocky Mountains rise abruptly from the plains and consist of a complex system of ranges, 75 to 175 miles (120 to 280 km) wide. Ranges in the east include the Front Range and parts of the Medicine Bow and Sangre de Cristo mountains. To the west lie the Park and Sawatch ranges and the northern part of the San Juan Mountains. The Continental Divide follows the crest of the higher ranges, separating waters that flow westward into the Pacific Ocean from those that drain eastward into the Mississippi River and Gulf of Mexico In Colorado, the area west of the divide is often called the Western Slope; the area east of it, the Eastern Slope.

Colorado's ranges, the highest in the Rocky Mountain system, contain more than 50 peaks exceeding 14,000 feet (4,267 m). Maximum elevations occur in the jagged Sawatch Range, where Mount Elbert reaches 14,433 feet (4,399 m). Only slightly lower are nearby Mounts Massive and Harvard. Probably best known of Colorado's summits is 14,110-foot (4,301-m) Pikes Peak, a semi-isolated peak in the Front Range.

Within the mountains, at elevations of 6,000 to 9,000 feet (1,830 to 2,740 m) are several broad, level basins, or parks. North, Middle, and South parks are enclosed mainly by the Front, Park, and Sawatch ranges. Farther south, between the Sangre de Cristo and San Juan mountains, lies the San Luis Valley. Part of the huge Wyoming Basin, which separates the southern and middle sections of the Rockies, extends into the northwestern part of Colorado.

The Colorado Plateau is an area of eroded tablelands 5,000 to 11,000 feet (1,520 to 3,350 m) above sea level south of the Wyoming Basin. The section lying in Colorado covers about a fifth of the state and consists mainly of Mesa Verde and the Uncompahgre and Roan plateaus.

Colorado's major rivers begin in the Rockies near the Continental Divide. The Colorado River, with such headstreams and tributaries as the Yampa, White, Gunnison, and Dolores, drains the Western Slope. The Eastern Slope is drained primarily by the South Platte and Arkansas rivers, which flow from the mountains across the Great Plains. The Rio Grande begins in the San Juan Mountains and drains the San Luis Valley. In the mountains and western plateaus many rivers have carved deep canyons and gorges. Among the most spectacular are the Black Canyon of the Gunnison and Royal Gorge on the Arkansas.

Numerous dams and reclamation projects on the rivers provide water for irrigation and municipal and industrial use; they also supply some hydroelectric power. The Colorado-Big Thompson and Fryingpan-Arkansas projects, two of the largest, divert water from the Western Slope, which has two-thirds of the state's surface water, to the Eastern Slope, where most of the population and farmland are concentrated.

There are hundreds of natural and man-made lakes in Colorado, all of them relatively small. The largest are impounded by dams and include Lake Granby and John Martin and Blue Mesa reservoirs.

The Rocky Mountains and the state's inland location are the major factors determining Colorado's climate. In general, the weather is dry and invigorating and is marked by abundant sunshine.

Climatic conditions are most uniform on the Great Plains. Winters here are cold, with January temperatures averaging between 25° and 30° F. (-4° and -1° C.). Periods of frigid weather, when temperatures drop to 0° F. (-18° C.) and below, alternate with relatively mild spells brought on by warm chinook winds that blow from the mountains. Summers are warm to hot, with average temperatures in July ranging from 73° to 79° F. (23° to 26° C.) and daytime highs of 90° F. (32° C.) or more. At high elevations near the mountains, nights are cool.

Precipitation in Colorado usually averages 10 to 15 inches (250 to 380 mm) a year, most of it coming as rain during spring and early summer. Droughts periodically strike the plains. They are most severe in the southeast, which was part of the Dust Bowl in the 1930's.

The climate of the mountains and the high western plateaus depends largely on elevation and exposure to sunlight and prevailing winds. In general, as altitude increases, temperature decreases and precipitation increases, but great variations may occur. Average temperatures at mountain stations range from 10° to 20° F. (-12° to -7° C.) in January and from 55° to 65° F. (13° to 18° C.) in July. Readings below 0° F. (-18° C.) are common in winter. Daytime highs in summer may reach 80° F. (27° C.) or more, but nights are quite cool. Most of central and western Colorado receives 15 to 25 inches (380 to 640 mm) of precipitation a year, with the greatest amounts falling as snow on the western slopes of mountains. In the San Luis Valley and parts of the Colorado Plateau annual precipitation totals less than 10 inches (250 mm).

Except in the mountains, the growing season usually lasts 120 to 180 days, depending on location and elevation.

Because of the variations in climate and altitude, Colorado has a great diversity of plant life. Forests, most of which are federally owned, cover about a third of the state, concentrated on the slopes of the Rockies and the higher parts of the Colorado Plateau. Conifers, including several species of pine, fir, and spruce, are the most numerous and economically valuable trees. Mixed with the conifers are stands of quaking aspen, a deciduous tree with leaves that turn brilliant gold in autumn.

Short grasses, such as buffalo grass and blue grama, once covered the Great Plains, but the spread of agriculture has destroyed much of this natural vegetation. Except for black willows and cottonwoods growing along the riverbanks, the plains are virtually treeless. Cactus, yucca, and other desert or semidesert plants grow in the drier parts of the state.

Hundreds of different kinds of wild flowers are found in Colorado. One of the most common and widespread is the Rocky Mountain columbine—the state flower.

Few states can match Colorado in the variety of its wildlife. Large animals include deer, elk (wapiti), pronghorns (antelope), black bears, bighorn sheep, mountain lions, and a few grizzly bears and bison (buffalo). Among the many birds found in the state are eagles, buzzards, sandhill cranes, road-runners, ptarmigans, wild turkeys, ducks, geese, and quail. Colorado lakes and streams abound with several kinds of trout and other freshwater fish.