Canyonlands National Park is drained entirely by the Colorado and Green Rivers, whose confluence is an important and scenic central feature of the park (figs. [59], [60]). Individual canyons traversed or drained by these rivers are discussed in later chapters.
When Major Powell reached the confluence in 1869, the river flowing in from the northeast to join the Green River was called the Grand River, and the Green and Grand joined there to form the Colorado River. The Grand River was renamed Colorado River by act of the Colorado State Legislature approved March 24, 1921, and by act of Congress approved July 25, 1921. But the old term still remains in names such as Grand County, Colo., the headwaters region; Grand Valley, a town 16 miles west of Rifle, Colo.; Grand Valley between Palisade and Mack, Colo.; Grand Mesa, which towers more than a mile above the Grand and Gunnison River valleys; Grand Junction, Colo., a city appropriately located at the confluence of the Grand and Gunnison Rivers; Grand County, Utah, which the river traverses after entering Utah; and Grand View Point, the southern terminus of Island in the Sky.
When viewed at a distance of 1 foot, the shaded relief map ([fig. 1]) shows the general shape of the land surface in and near Canyonlands National Park to the same horizontal scale as it would appear to a person in a spacecraft flying at a height of 250,000 feet, or about 48 miles. This map was prepared by artist John R. Stacy from parts of the reverse sides of four plastic relief maps[2]—Salina, Moab, Cortez, and Escalante quadrangles, at a scale of 1:250,000—using a simple time- and money-saving method he devised (Stacy, 1962).
An image of Canyonlands National Park and vicinity from a satellite at a height of about 570 miles is shown in [figure 7]. Note white clouds and black cloud shadows on right.
CANYONLANDS NATIONAL PARK AND VICINITY, from NASA’s unmanned Earth Resources Technology Satellite (ERTS-1), at height of about 570 miles. The space image map was prepared from simultaneous scanning in three color bands—blue green, red, and near infrared—that were combined to produce a false-color image in which vigorous green vegetation (forests and irrigated areas) appears bright red, water dark blue, and soils and bare rocks various shades of blue, blue green, or yellow green. Bright-blue area on west bank of Colorado River about 10 miles southwest of Moab is the group of large evaporation ponds of Texas Gulf, Inc., shown in figures [31] and [71]. Images were taken at 10:31:10 a.m., Aug. 23, 1972, during the 432d orbit, telemetered to Alaska, videotaped, then photographed. Sun elevation was 53 degrees above horizon from azimuth of 130 degrees. Image covers an area about 100 miles square. (See scale.) Location of Monticello is approximate; that of other towns is believed to be correct. Park boundaries are not shown because of difficulty in locating them accurately, but features such as Colorado and Green Rivers can easily be compared with those in [figure 1]. (Fig. 7).
Rocks and Landforms
The vivid and varied colors of the bare rocks and the fantastic canyons, buttes, spires, columns, alcoves, caves, arches, and other erosional forms of the canyon country result from a fortuitous combination of geologic and climatic circumstances and events unequaled in most other parts of the world.
First among these events was the piling up, layer upon layer, of thousands of feet of sedimentary rocks under a wide variety of environments. Sedimentary rocks of the region are composed of particles ranging in size from clay and silt through sand and gravel carried to their resting places by moving water, silt and sand particles transported by wind, and some materials precipitated from water solutions, such as limestone (calcium carbonate), dolomite (calcium and magnesium carbonate), gypsum (calcium sulfate with some water), anhydrite (calcium sulfate alone), common salt (sodium chloride), potash minerals such as potassium chloride, and a few other less common types. Some of the materials were laid down in shallow seas that once covered the area ([fig. 8]) or in lagoons and estuaries near the sea. Some beds were deposited by streams in inland basins or plains, a few were deposited in lakes, and some, like the Navajo Sandstone, were carried in by the wind. The character and thickness of the sedimentary rocks, and the names and ages assigned to them by geologists, are shown in the rock column in [figure 9] and in the cross sections in figures [10] and [15], and the history of their deposition is discussed in the chapter “Summary of Geologic History.” The rock column was compiled mainly from generalized stratigraphic sections given by Baker (1933, 1946), McKnight (1940), Hinrichs and others (1967, 1971b), and F. A. McKeown and P. P. Orkild (U.S. Geol. Survey, unpub. data, Mar. 16, 1973).