Oil and gas production in Colorado is decreasing at present, even though great efforts are being made to find new oil pools. Petroleum prospecting and wildcat drilling are carried out in as yet unproductive basins in the Plateau Province, in intermontane basins such as the San Luis Valley, and on the Plains. Known reserves will continue to provide the state with significant income for many years to come, and if oil shale recovery becomes profitable. Colorado’s hydrocarbons will become the most prominent of her commodities. COAL Coal resources of Colorado amount to about 60 billion tons. Only one per cent of this has been mined. Thousands of tons are now being produced daily from large mines in central, southern, and northwestern parts of the state. Colorado’s coal deposits were formed during late Cretaceous and early Tertiary time, when seas were receding from this region and the land was rising. They represent accumulations of leaves and other plant material in swamps and flood plains similar to those now found in the delta of the Mississippi River and in the swamps of southeastern United States. Almost all Colorado coal is bituminous or soft coal. Coal was recognized early in Colorado history by settlers along the mountain front, and was mined west and north of Denver in the 1860s. Several large underground mines still operate in this district, supplying local power plants, but production does not compare with that of the Walsenburg-Trinidad area in southern Colorado or the Hayden area in northwest Colorado. The Walsenburg-Trinidad region, part of the Raton coal field, has produced coal since the building of the Santa Fe Railroad in the early 1870s. For many years coal from these mines moved the Santa Fe trains and many of the numerous smaller railroads that served Colorado’s cities and mining camps. The location of the mines helped to determine the location of the Colorado Fuel and Iron Company smelter in Pueblo. Now, most southern Colorado coal is used to produce electric power. Many small mines, miles away from the power plant west of Trinidad, are deserted. A large coal-burning power plant has recently been built between Hayden and Steamboat Springs, just west of the Yampa River. Here, some of the extensive coal deposits can be seen in road cuts along U. S. highway 40. Until conversion to diesel fuel became almost universal in North American railroads, mines of this district produced coal for locomotives. In the heyday of the gold and silver mines, coal was also mined near Coalmont, in North Park, and Como, in South Park. Coal from these areas was used for fuel in nearby mining towns and ranches, and for the narrow-gauge railroads that penetrated the mountains here.