Colorado Plateau

“ 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 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. ”

“ 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 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 ”

“ 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. ”

“ One range roughly paralleled the present Front Range, but lay thirty to fifty miles further west. The other extended from the San Luis Valley northwest toward Colorado National Monument, including the area around the Black Canyon of the Gunnison and the present Uncompahgre Plateau. Coarse sediments washed off both sides of both ranges, and accumulated as alluvial fans and valley fill along the mountain margins. These exist today as the Fountain Formation of the eastern Front Range, the Minturn Formation between the ancient uplifts, and the Hermosa Formation west of the western uplift. ”

“ In recent years Colorado’s prairies, peaks, and plateaus have brought new meaning to all America: the state now provides an attractive playground for state residents and their visitors. Campgrounds, streams, lakes, and high trails beckon in summer; barren slopes deep in winter snow attract the skier. More and more, those who live in Colorado and those who visit her seek to understand these mountains and hills and prairies, to learn of her geologic origins and her far distant past. ”

“ 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. ”

“ Where the sand is dropped, the dunes have formed. They rise to about 700 feet above the valley floor, and cover about forty square miles. The low rainfall of the area, seven to eight inches per year, keeps vegetation from creeping over the dunes and makes them a most distinctive feature of Colorado, a lesson in geology in the making. ”

“ We found much to interest us in Colorado Springs. It is a town of great fame as a health resort, and lies on a splendid plateau, with the background of the Rocky Mountains, and Pike's Peak, in all its snowy splendor, in the middle distance.
Near by is Colorado City, and joining on to that is Manitou, where lie the wonderful mineral springs, from which the city of "Colorado Springs" gets its name.
The wise men who founded the city, knew well that there was no room for expansion in the Alpine clefts where the springs lie; and yet they knew, too, their value as an attraction. ”

“ 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. ”

“ 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 Colorado in its course below the junction has formed a region that is one of the most wonderful of the world, not only for its unique and magnificent scenery, but also because it affords the most remarkable example known of the work of differential weathering and erosion by wind and water and the exposure of geologic strata on an enormous scale. Above the Paria the river flows through scenery comparatively tame until it reaches the plateau of the Marble Canyon, some 60 m. in length. The walls here are at first only a few score of feet in height, but increase rapidly to almost 5000 ft. ”

“ 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. ”

“ On the cast the great plateau breaks down in a very irregular way into the valley of the Little Colorado, and where the railroad ascends the plateau from the east it passes over picturesque canyons that run down into the Little Colorado. On the south the plateau is merged into the great system of mountains that stand in Southern Arizona. Where the plateau ends and the mountains begin is not a well-defined line. The plateau through which the Grand Canyon is cut is a region of great scenic interest. ”

“ There are two grand divisions: the lowland or desert, below the Virgen, and the plateau, but the topography of the immediate river course separates itself into four parts, the Green River Valley, the canyon, the valley-canyon, and the alluvial. The canyon part is the longest, occupying about two-thirds of the whole, or about 1200 miles. It is cut mainly through the plateaus. The last of these southward is the Colorado, a vast upheaval reaching from the lower end of the Grand Canyon south-east to about where the 34th parallel crosses the western line of New Mexico. ”

“ Not to seem too technical, the top stratum, that is to say the rock immediately under the soil of this plateau, while quite hard, is very thin, and underneath it are various other layers of rock, some fairly hard and others very soft. The Colorado River has a very swift current, and once it had cut through the hard rock on the top it quickly ate its way downward through the soft limestones and sandstones below. But some strata were quite hard and these, resisting the water, formed the terraces which you see on every hand. ”

“ The water cuts out the light soil and also heaps it up. In the canyons the river runs 6,000 feet below the level of the plateau, and people on the desert above might die with thirst because of the impossibility of getting down to the water.
The Colorado is forever changing its course and currents. Here mud flats are forming, there a bank is being washed away. Here a mighty rock topples into the stream, there the water cuts around a tower, leaving a pillar three hundred feet high, standing out alone! The river, ages ago, entered the Gulf of California where Yuma is now ”

“ The sea continued to cover most of Colorado after the end of the Devonian Period, well into Mississippian time. Mississippian rocks are characteristically thick, massive gray limestones collectively called the Leadville Limestone. This unit is well known as the host rock for many Colorado ore deposits, notably those around the town of Leadville.
During Mississippian time the western sea, warm and rich in organisms, covered much of North America. Brachiopods and corals flourished, as did many other forms of life. ”

“ On the east the Little Colorado comes; here it is a river of salt water, and it derives its salt a few miles up the stream. The main Colorado flows along the eastern and southern wall, Climbing this for a few hundred feet you may look off toward the northwest and gaze at the cliffs of the Kaibab Plateau.
This is the point where we built a trail down a side canyon where Mr. Walcott was to make his winter residence and study of the region; it is very complicated and exhibits a vast series of unconformable rocks of high antiquity. These lower rocks are of many colors ”

“ In the north there is an extensive but barren plateau, with an average elevation of 7000 feet, through which the Colorado cuts its way, and forms one of the most remarkable gorges in the world, the length being about 300 miles, and the perpendicular walls reaching heights of from 3000 to 6000 feet. ”

“ Only part of the earth’s very early history is represented in Colorado, where the oldest known rocks are the gneisses and schists of the Idaho Springs Formation, at least 1,800,000,000 years old. These rocks appear to be the remains of ancient sediments, folded and metamorphosed into vast mountain areas long before recognizable life inhabited the earth. ”

“ From clay to gold, much of Colorado’s wealth has come from her mountains. But after the rush to the mines, as veins were mined out and placers worked over, as values and prices changed, her population sought the riches of the prairies: fertile lands for agriculture, and in the rock layers below, black gold—vast accumulations of oil and natural gas. The tablelands and plateaus west of the mountains yield their wealth, too. Here are valley farms, fed often by irrigation water, and ranch country. Here is more oil, and in some areas precious metals and uranium. ”

“ In the lower right-hand comer are the Yosemite Valley and the Gorge of Niagara on the same scale. The scale of this reduction is about 14 miles to one inch. The vertical and horizontal scales are the same. The black ribbon on the left at Virgen and Beaver Dam Mountains is to represent Archæan formation. The Shiwits Plateau and Uinkaret Mts. are basaltic. The Kaibab and the Colorado Plateau are Carboniferous. Paria Plateau and Vermilion Cliffs are Triassic. The Markagunt and Paunsagunt Plateaus are Tertiary. Cardenas reached the canyon about at letter “A” of the word “Cañon.” ”

“ Beneath the flat prairies of eastern Colorado, sedimentary rocks form a series of layers. Those near the surface are among the youngest rocks in Colorado. We know this from the fossils they bear, fossils of large mammals such as the hairy mammoth, which lived in early Quaternary time, the bison, and many smaller mammals living today.
The layers below—sandstones, shales, and limestones—become progressively older as one goes deeper. ”

“ Moisture carried by prevailing westerly or northwesterly winds falls primarily on Colorado’s western slope, although at some times of year precipitation may come from the northeast or southeast. West of the continental divide, where population is sparse, there is a surplus of water. East of the divide, where more than 90 per cent of the population lives, water is in desperately short supply. ”

“ Colorado is rich in mountain scenery and in beautiful camping places for the lover of hills and streams, the pedestrian and the fisherman.
We came down from the high plateau of the Park by the canyon of the Little Thompson; a still more [Pg 186] precipitous road than that of the Big Thompson Canyon. Reaching Lyons, we turned toward Boulder, driving along with alfalfa meadows to the left and the foot hills of the Rockies to the right. Our undulating road was an excellent one. ”