Halka Chronic

“ The ranges of the Colorado Rockies form rank upon rank of ridges and peaks, roughly north-south in trend, about 100 miles across from east to west, extending from the northern to the southern border of the state. Here, in mountain springs and lakes, are born the rivers of Colorado: the Platte, the Arkansas, the Yampa, the Colorado. Crags and cliffs tower above tree-covered slopes, the rocks always a dominant part of the landscape. The continental divide runs through the state along the summit ridges. West of the divide, all streams flow to the Colorado River and the Pacific ”

“ Bordering the western side of North, Middle, and South Parks, another long north-south trending ridge extends from the Wyoming border toward the center of Colorado. The northern part of this ridge, forming the western boundary of the main mountain mass in the state, is called the Park Range.
The structure of the Park Range is similar to that of the Front Range: a huge linear corrugation in the earth’s crust, bounded by faults. Because this area has fewer resistant sedimentary rock layers above the Precambrian basement rocks, it is not prominently edged with upturned sedimentary layers. ”

“ 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. ”

“ Our present distribution of population is partly a heritage from these first settlements, partly a result of later discoveries of oil, gas, and radioactive minerals, and partly a response to the state’s extreme topographic variation, which controls and delineates agricultural areas and transportation routes.
In recent years, man has begun to appreciate the fact that he may benefit in other ways from knowledge about geology. A new geology has developed—environmental geology—which may be defined as the total of all geological conditions and influences affecting the life and development of man. ”

“ Exhausting the placer sands of the stream bottoms, they moved higher to mine gold-bearing veins at Central City and Blackhawk. Mining camps sprang into existence overnight, each heralding some new “strike,” each populated by a new rush of fortune seekers. As lower areas were mined out, prospectors moved yet higher—to Breckenridge, Gold Hill, and Empire, Aspen, Leadville, and Cripple Creek. Silver was found as well as gold, then iron, and later tungsten and molybdenum. The metallic ring of mining tools echoed from Colorado’s peaks. ”

“ Precambrian rocks in Colorado are on the whole very poorly known. They have, however, been studied in detail in the Front Range west of Denver and Boulder, where they have been intensively explored for valuable minerals. The lack of fossils in the oldest rocks makes their close correlation difficult, but from studies of radioactive minerals contained in these rocks, and of the relationships of the rock units themselves, we can list them in order of their relative ages. ”

“ Something can be told of the age of the continents. Measurements of radioactivity in the most ancient rocks exposed at the surface today indicate that the oldest known continental rock is between three and four billion years old. Since the continents were formed, they have been bent and shifted and broken by the pressures exerted against them by convection in the interior. Parts of the continents at times have been submerged below the level of the sea, even as they are today. Other portions, lifted above sea level, were immediately attacked by the wearing-down processes of erosion. ”

“ The light of day revealed the nature of the destruction—mud in every nook and cranny, soggy merchandise, warped bowling alleys, drowned animals, the loss of irreplaceable possessions, to name a few types. ”

“ In the Plateau Province another type of cave is formed not so much by groundwater as by weathering of the flat-lying alternating beds of massive resistant sandstone and less resistant, thinly 108 bedded mudstone and shale. Where the resistant layers are undermined, great arching caves develop. These are best observed at Mesa Verde National Park, where many of them once sheltered Indian communities. They can also be seen in Colorado National Monument and along the Colorado River and several of its major tributaries. ”

“ 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. ”

“ Two aspects of environmental geology which are particularly pertinent to Colorado’s residents are discussed below.
Landslides and slumping rock or earth are a frequent menace to Colorado’s development in the Mountain Province. Often activated by heavy rains or deep manmade cuts, they can cause—and have caused—much damage to roads, buildings, and other works of man.
The flanks of North and South Table Mountains, near Golden, are mantled by thick landslide debris; intermittent movement of the individual slides has repeatedly affected the railroad, irrigation ditches, and roads. ”

“ 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. ”

“ 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. ”

“ In the northeast part of the mineral belt, gold and other minerals occur in veins in Precambrian granite and gneiss. In the Leadville and Aspen areas, ores are associated with altered Paleozoic limestones. At the southwest end of the mineral belt, in the San Juan Mountains, ore veins are found near or in Tertiary volcanic rocks. Native gold, gold-bearing compounds, and other metallic ores in these veins originated where mineral-rich solutions from deep within the earth penetrated fissures and joints in the surrounding rock. ”

“ The rocks deposited in western Colorado at this time are markedly different from those deposited in eastern Colorado. In the east, deposits are fine and very limy, containing abundant shells and little in the way of coarse debris. In the west, sandstones of the Mesa Verde Formation dominate, and coal beds suggest marshy or swampy conditions inshore from the ancient ocean. This is just the pattern we would expect from a low-lying region bordering a shallow sea, a region similar perhaps to the southeastern Atlantic and Gulf coasts of the United States today. ”

“ The mountains thus formed are known to geologists as faulted anticlines.
As the mountains rose, they were of course attacked by the forces of erosion. The sedimentary layers were completely stripped from the crests of many of the uplifts, so that Precambrian rocks were exposed. It is these rocks which form the summits of the highest peaks of Colorado. As with all rules, there are exceptions: the Spanish Peaks are volcanic, and the crest of the Sangre de Cristo Range is composed of sedimentary rocks. ”

“ The multitudes of mineral and hot springs in Colorado are a fascinating and interesting facet of the Mountain Province. Some are located along major faults, where the rocks are so broken and shattered that groundwater can move freely toward the surface. Colorado Springs, Manitou Springs, and Eldorado Springs are on the fault complex that forms the east edge of the Front Range. ”

“ Most of the rich mineral deposits of Colorado are thought also to have been formed during the early part of the Tertiary Period. Solutions rich in gold, silver, zinc, lead, copper, and sulfides of iron seeped into joints and faults in the crust as the mountains were pushed upward. Ore minerals crystallized out, sometimes in veins in the ancient Precambrian igneous and metamorphic rocks, sometimes in Paleozoic sediments. ”

“ Concentrations of uranium often occur in or near organic matter such as coal, fossil bone, or petrified wood, so mines tend to be located along rock layers carrying abundant organic material.
Another type of uranium ore is found in the Mountain Province. Veins in Precambrian rocks of the Front Range and several other ranges contain pitchblende which seems to have been deposited by hot groundwater rising through broken and fissured Precambrian rocks. Often exceedingly rich, such ore is mined in the manner of most of Colorado’s metals. ”

“ Torrential erosion—spring floods and summer thunderstorms—has deeply furrowed the prairie surface here and left these buttes as lonely sentinels.
This map shows the distribution, character, and thickness of certain Jurassic rocks in Colorado. These rocks are deeply buried beneath the plains and are known there only from well samples. They have been eroded from most mountain areas. They come to the surface along the edges of the mountains and in the deeply incised canyons of the Plateau Province. ”

“ As the Pennsylvanian Period began, the Colorado area continued to rise. Earliest deposits of this age are fine-grained black shales and sands—the Glen Eyrie Formation along the southern Front Range and the Belden Formation in west central Colorado. Then, through millions of years, mountain-building took place. Some areas rose more than others, so that formerly flat-lying marine sediments were bent and broken, and a series of high mountain ridges and deep basins were formed. Geologists sometimes call these the Ancestral Rocky Mountains. ”

“ The recent rise in the price of silver has encouraged many miners to reopen old shafts. The most active mines in the state today are those producing molybdenum, lead, zinc, and vanadium. (Vanadium, although a metal, usually occurs in Colorado with 78 radioactive minerals, and so is discussed with them rather than with the metals.)
The Colorado mineral belt extends from Boulder County on the northeast to San Juan County on the southwest. Almost all of the prominent mining districts in Colorado lie along this belt. ”

“ The climate of the entire earth appears to have been warmer then than it is at present, perhaps because of a different distribution of land and sea areas, or because continental areas were not as high and mountainous as they are just now. Colorado was a rather low land area for most of the first two Mesozoic periods; then a vast sea covered the entire state for the remainder of the era.
The pink cliffs of Colorado National Monument are made of Wingate and Entrada Sandstones. Underlying them, in the valley bottom, Chinle shales form steep red slopes. ”

“ In central Colorado, the lowest Mesozoic deposits are the Triassic Lykins Formation, a series of soft, bright red sandstones and shales. Where the Lykins is exposed along the Front Range, its bright 52 red color identifies it. Because of its softness, it is often less prominent than adjacent rock layers in the mountain foothills. The Lykins Formation includes some evaporites, apparently derived from Permian evaporites washed into the Triassic ponds and lakes which existed occasionally in this region. ”

“ Water problems in Colorado revolve mainly around the best use of runoff in a state whose major catchment basins are across the continental divide from her largest population centers and most fertile farm land. Groundwater, closely related to surface water distribution and movement, is a geological problem, and in Colorado as in other states many government and private geologists serve farm and industrial communities in the search for usable supplies. ”

“ As gold sources were depleted, silver, first produced as a byproduct, became of prime interest. Lead and zinc were in turn byproducts of silver mining. Other metals, notably copper, vanadium, tungsten, and iron, were produced later. Molybdenum is the Johnny-come-lately of the state’s mining industry, but is 75 now the chief metal produced. A uranium boom in the 1950s brought a short rush to western Colorado and new vigor to the economy. ”

“ Placer gold has always been the principal mineral product of the Fairplay area, but native gold also occurs in the surrounding mountains in quartz veins, and many small mines were developed to extract it. Sulfide ores were also mined; they contained silver, lead, and zinc as well as gold. In the Mosquito Pass and Horseshoe Amphitheater areas, there is renewed activity now because of the recent rise in the price of silver. ”

“ The sandstones derived from beach sands sometimes include coarse pebbles of chert which can be traced to sources in Permian rocks of Utah and Nevada. Occasionally the beach and near-shore deposits include marine shells like oysters, indicating that there were brackish and salt water lagoons and marshes along the shore. The Dakota Formation represents the beach of the transgressive or advancing sea. This formation contains oil in eastern Colorado, Nebraska, and Wyoming; the oil itself may have been 57 derived from decay of organic materials in swamps behind the beaches and bars. ”