The State's primary source of wealth, the foundation of its economy (see The Economic Base), is its farm and pasture land comprising not quite three-fourths of its 66,341,120 acres. Approximately 32,000,000 acres are suitable for grazing, most of which are in use; some 13,000,000 acres can be farmed, but little more than half are under cultivation. A wide variety of fertile soils, usually rich in mineral matter but deficient in humus, and ranging in texture from sandy loams to refractory clays and adobes, characterizes the arable lands. The climate, one of the State's chief attractions, is generally mild and sunny, but varies considerably from one section to another, influenced in large part by wide differences in altitude. From the State mean of 44.9 degrees, local average temperatures range upward to 54.4 degrees at Lamar in the lower Arkansas Valley and downward below the freezing point on the Alpine meadows at the top of the Continental Divide. Agriculture on the lower Western Slope is favored by a growing season of 186 days, while at Pagosa Springs near the base of the San Juans only 76 days normally intervene between killing frosts. In Leadville, at the headwaters of the Arkansas, snow has fallen more than once on the Fourth of July. Annual precipitation ranges from as little as seven inches in the San Luis Valley to almost twenty-seven inches at Silverton in the towering San Juans; the State mean is 16.62 inches. As rainfall in most farm areas is deficient, elaborate irrigation systems are required to water almost all lands off the main watercourses. Fields irrigated with water drawn in ditches or flumes from running streams, lakes, reservoirs, and artesian wells aggregate some 3,400,000 acres, or more than a fourth of all farm lands in the State. Only California exceeds Colorado in irrigated area.

Colorado ranks eleventh among the States in potential water power, estimated at 2,568,000 horse power, of which a mere 103,000 has yet been harnessed. Running streams can generate 765,000 horse power the year round without mountain dams and reservoirs. Wind power, although too uncertain for industrial use, has been of great value in pumping water for livestock on the arid plains, and high wind velocities on mountain peaks may perhaps prove an abundant source of energy in the future.

Immense mineral deposits underlie widely scattered areas in central and western Colorado. Roughly, the largest metal mining region extends along the Continental Divide from the golden "Kingdom of Gilpin," in the mountains west of Denver, to the headwaters of the Rio Grande and into the San Juans in the southwestern corner of the State. The rich Cripple Creek gold fields lie isolated in the tiny crater of an extinct volcano behind Pikes Peak; also isolated are the vanadium and uranium beds in Paradox Valley along the Utah boundary. The extent of the metal reserves in the Colorado Rockies is unknown, for many veins have merely been tapped and others are constantly being discovered. As the mountain-making process cracked, broke, and telescoped rock strata throughout the mining area, leaving innumerable crevices, fissures, and reverse faults, prospecting has posed problems often less successfully solved by strictly scientific method than by the trial-and-error system necessarily employed in piecing together a baffling jig-saw puzzle. But in spite of all natural obstacles, Coloradoans have already dug and blasted $3,000,000,000 of precious and industrial metals from the granite warehouses of the Rockies. More than 250 useful minerals have been discovered within the State, and approximately 35 are now being extracted for market. Colorado stands first among the States in the extraction of such rare minerals as molybdenum and uranium, third in gold, fourth in tungsten, fifth in silver, sixth in lead, seventh in copper, and fifteenth in zinc.

Colorado ranks first among the States in coal reserves, being credited by the United States Geological Survey with 417,982,149,000 short tons bedded in an area of 19,754 square miles; these are sufficient at the present rate of consumption to supply the entire Nation for seven centuries. On the Western Slope are three large fields—one in Moffat County in the northwestern corner of the State, another about midway along the Utah border, and the third in the San Juan Basin to the southwest. The eastern coal beds stretch in a broken and irregular chain along the foothills from Wyoming to New Mexico. At their southern extremity, in and around Trinidad, are great bodies of iron ore, but these have proved more costly to work than deposits in neighboring States.

Twelve productive and extensive oil fields have been discovered in widely scattered parts of Colorado since petroleum was first found in the Arkansas Valley, near Florence, in 1862. More important, however, is the petroleum locked in the Federal Government's reserve of 952,239 acres of Tertiary oil shale in Mesa, Garfield, and Rio Blanco Counties on the Western Slope. The Federal Oil Conservation Board estimates that these shales contain 47,625,598,000 barrels of recoverable oil, equivalent at the present rate of production to the country's entire output for half a century. Natural gas has been discovered over a wide area, but only the wells around Craig in the northwestern coal fields are of importance. Carbon dioxide gas has been found in Jackson County near by, but efforts to separate it from the petroleum with which it is combined have been unsuccessful. Helium gas has been struck in Las Animas County on the southern plains, and in western and northern Colorado, but as the Federal Government does not permit its export, the wells have been capped.

The quantity, quality, and infinite variety of Colorado stone— granites, marbles, limestones, sandstones, and lavas—are known to builders and architects throughout the world. Decorative marbles occur in Wet Mountain Valley and along the upper Arkansas on the Eastern Slope, and at Marble on the Western Slope. Large clay beds near Denver and elsewhere have given rise to many important manufactories of pottery, brick, tile, terra cotta, and similar products.

Colorado has fourteen national forests entirely within the State and one extending across the western boundary into Utah. These forests embrace 13,552,021 acres, with an estimated stand of 39,918,969,000 board feet of merchantable timber. State nurseries replace losses from fires at the rate of several million trees a year. The annual growth of the forests approximates 500,000,000 board feet, of which little more than a tenth is cut yearly. But the forests with their plant and animal life serve a far more important purpose than timber production; they are of inestimable value in forwarding conservation, recreation, and the general health and welfare. They are the great natural reservoirs that store the water upon which Coloradoans so largely depend; they provide the summer playgrounds upon which are based the State's largest "industry," tourist travel.