Part 13

Petroleum and natural gas have been found in large quantities in the Prairie and Plateau Provinces in Colorado, as well as in smaller quantities in North Park in the Mountain Province. They generally occur in porous sandstone and limestone layers, where they have been trapped by overlying finer-grained, less permeable layers in or near folds and faults.

Several oil and gas seeps were found along the mountain front shortly after the arrival of the earliest settlers. Near Canon City, on Oil Creek, a plaque commemorates the first production:

Oil Creek—site of the first oil well in the west—second place in the United States to produce petroleum from wells. In 1862 ... A. M. Cassedy drilled an oil well 50 feet deep. By February, 1863, production was one barrel a day. Later, several thousand gallons of petroleum were produced by primitive methods, and kerosene and lubricating oil were shipped by ox team as far as Denver and Santa Fe.

About twenty miles to the southeast, near Florence, the Cretaceous Pierre shales were drilled in 1876. Oil was found in a system of intersecting fractures and joints. Some of the early wells in the Florence field are still producing, making this Colorado’s oldest and longest producing field. It has yielded more than 10,000,000 barrels of oil.

Small quantities of oil have been produced near Boulder since about 1900, also from Pierre sandstones and shales. In this area, wells were located by “dowsing” or “witching,” as was fashionable at the time. Several old rigs can be seen near Boulder Reservoir. As at Florence, oil has been trapped in fractures of otherwise dense and impervious shale. Some gas is produced and is used by local farms.

More recently, oil was found far beneath the surface in the northern part of the Prairie Province. Here, in the Denver Basin, oil is produced from several levels in the Dakota Sandstone. The oil has accumulated in lenses of beach sand deposited along the shoreline of the Cretaceous sea. The general trend of the shoreline, and of the oil fields, is northeast-southwest. The shore appears to have been similar to Georgia’s present coastline: a swampy tidal zone separated from open sea by lagoons, sandy bars, and clean sand beaches.

Individual oil pools in the Denver Basin are small, but there are many of them; they lie nearly a mile below the surface, under much of Morgan and Logan Counties and adjacent parts of Nebraska. Exploratory and development drilling keeps total oil production at about 50,000 barrels a day. Oil and gas produced here is piped to Denver and other Colorado cities.

In southeastern Colorado, oil and gas occur in late Paleozoic limestones and sandstones similar to those which outcrop at the edge of the Wet Mountains. Prospecting by geophysical methods and by drilling has revealed several small, rich accumulations, one of which is thought to contain about 30,000,000 barrels of oil.

The Rangely field, in northwestern Colorado, is the most productive field in the state. Located in the northeastern part of the Uinta Basin, it is an outstanding example of an anticlinal field, where oil is trapped in a large, gentle dome. The shape of the dome shows up well on the surface; rock layers can be seen dipping outward in all directions from the town of Rangely. Oil was found by drilling on the crest of the dome. At first, oil was produced from fractures in the Cretaceous Mancos Shale at less than 1,000 feet depth. Later, deeper drilling showed that oil had also accumulated in the Permian Weber Sandstone, at 5,000 to 7,000 feet. At present this field is producing about 28,000 barrels of oil a day, but the figure is dropping each year as the field is depleted.

Oil and gas are produced in southwestern Colorado from the eastern edge of the Paradox Basin and the northern edge of the San Juan Basin. In the Paradox Basin, oil comes from Pennsylvanian limestone mounds or reefs. Production in the Colorado part of the basin has been at most a few thousand barrels per day; more is produced in adjacent Utah. In the San Juan Basin, gas and oil are trapped in thin porous layers of Cretaceous and Pennsylvanian sandstone, between impervious layers of shale. Most of the production is in New Mexico, although some oil comes from the Colorado part of the basin.

The greatest known potential oil resource in the world lies in the oil shales of western Colorado. The richest of these shales cover an area of 1,600 square miles north of the Colorado River, south of the White River, and just east of the Colorado-Utah line. The oil shales are part of the Tertiary Green River Formation, which extends over much of northwest Colorado, northeast Utah, and southern Wyoming. Oily material called kerogen is locked in these rocks, too solid to flow out of the fine pore spaces of the shale. To free it the shale must be mined, finely crushed, and heated until the kerogen converts to liquid oil. This is an expensive process, and as yet production of petroleum from the oil shale has not been possible at a cost which will compete with production of oil and gas from wells. The United States Bureau of Mines, as well as a number of oil companies, have sought for more than fifty years to discover a less expensive method for extracting oil from the shale. No doubt at some time in the future a competitive technique will be developed, or a growing shortage of other oil will bring world prices to a level with which present production techniques can compete.

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.

At Anthracite, near Crested Butte, high-grade anthracite coal was mined for a time. Identical in origin with other Colorado coal, the anthracite of this region was hardened by heat and pressures from Tertiary igneous intrusions forcing their way into local sedimentary rocks during post-Cretaceous mountain building.

A multitude of other coal camps are scattered about Colorado: Cokedale, Delcarbon, Coaldale, Roncarbo, Carbondale, and Cardiff stand out because of their suggestive names. These early small camps are, like their metal-mine cousins, largely deserted today.

CONSTRUCTION MATERIALS

Sand, Gravel, and Clay

Sand, gravel, and crushed rock rate high among geologic products in Colorado; more than $27,000,000 worth of these materials were produced in the state in 1969. Highway and construction activities have brought recent expansion in the number and size of quarries and gravel pits. Increasingly, Coloradoans are insisting that quarries and pits be excavated only where they will not mar the natural beauty of the landscape, and many old pits are now being filled in. Unfortunately, the scars left by some quarries—such as that on the Rampart Range near Colorado Springs—are difficult to erase.

Clay of good quality occurs in Cretaceous deposits in many parts of Colorado, most frequently in the Dakota or Laramie Formations. In the area around Golden, the Coors Porcelain Company for many years mined clay for use in pottery and low temperature ceramic ware. Scars from this mining can be seen along the mountain front north and south of Golden, and deep clefts within the town, just west of Colorado School of Mines, testify to the amounts of clay that have been removed. Colorado clay is not pure enough to be used in high temperature ceramics, and the present use for it is in the manufacture of common tiles and bricks.

A recent development in Colorado is the use of Cretaceous Pierre shales in manufacturing lightweight aggregate for building. The shale is mined between Golden and Boulder, near Colorado highway 93. In the nearby plant, it is pulverized and then heated in a large rotating cylinder until the surface of each particle fuses. Then the particles are quickly cooled. The resulting product is much like cinder, light in weight and yet strong. It can be mixed with cement for use in construction work requiring a great strength-to-weight ratio, or made into concrete blocks.

Stone

In Colorado, as in most parts of the world, building stone for local use is quarried locally. Two of the state’s stones, however—Yule Marble from the Crystal River Canyon, and Lyons Sandstone of the Front Range—have been more widely used.