The district of country lying south of the Tavaputs table land, and east and south of the High Plateaus, is traversed by many deep cañons. This is the Cañon Land of Utah. In its midst the Green and Grand unite to form the Colorado. The Price and San Rafael are tributary to the Green. The Fremont, Escalante, Paria, Kanab, and Virgin are directly tributary to the Colorado from the north and west. From the east the San Juan flows to the Colorado, but its drainage area is not included in our present discussion.
West of the lofty zone lie low, arid valleys, interrupted by short and abrupt ranges of mountains whose naked cliffs and desolate peaks overlook the still more desolate valleys. These short longitudinal ranges are but a part of the Basin Ranges, a mountain system extending through Nevada and northward into Idaho and Oregon. That portion of the Basin Range System which lies in Utah, and which we now have under consideration, is naturally divided into two parts, the northern embracing the drainage area of Great Salt Lake, the southern embracing the drainage area of Sevier Lake, giving the Great Salt Lake District and the Sevier Lake District.
To recapitulate, the grand districts into which Utah is naturally divided are as follows: The Wasatch Mountains and the High Plateaus, constituting the lofty zone above mentioned; the Uinta Mountains, the Tavaputs table lands, the Uinta-White Basin, the Cañon Lands, the Sevier Lake Basin, and the Great Salt Lake Basin, the two latter being fragments of the great Basin Range Province.
The eastern portion of the Territory of Utah is drained by the Colorado River by the aid of a number of important tributaries. The western portion is drained by streams that, heading in the mountains and high plateaus of the central portion, find their way by many meanderings into the salt lakes and desert sands to the westward.
Considered with reference to its drainage, Utah may thus be divided into two parts—the Colorado drainage area and the Desert drainage area; the former is about two-fifths, the latter three-fifths of the area of the territory.
All of the Wasatch Mountains lie west of the drainage crest; a part of the High Plateaus are drained to the Colorado, a part to the deserts. This great water divide, commencing north of the Pine Valley Mountains in the southwest corner of the territory, runs north of the Colob Plateau and enters the district of the High Plateaus. It first runs eastward along the crest or brink of the Pink Cliffs that bound the Markagunt and Pauns-a-gunt Plateaus, and then north and east in many meandering ways, now throwing a plateau into the western drainage, and now another into the eastern, until it reaches the western extremity of the Tavaputs table lands. Thence it runs around the western end of the Uinta Valley, throwing the Tavaputs table lands, the Uinta Valley, and Uinta Mountains into the Colorado drainage, and the Wasatch Mountains into the Desert drainage.
These two regions are highly differentiated in orographic structure and other geological characteristics. The sedimentary formations of the eastern region are in large part of Cenozoic and Mesozoic age, though Paleozoic rocks appear in some localities. The Cenozoic and Mesozoic formations are largely composed of incoherent sands and shales with intercalated beds of indurated sandstone and limestone. The great geological displacements are chiefly by faults and monoclinal flexures, by which the whole country has been broken up into many broad blocks, so that the strata are horizontal or but slightly inclined, except along the zones of displacement by which the several blocks are bounded. Here the strata, when not faulted, are abruptly flexed, and the rocks dip at high angles.
The Uinta Mountains are storm carved from an immense uplifted block. The mountains of the Cañon Lands are isolated and volcanic. In the High Plateaus sedimentary beds are covered by vast sheets of lava. The sedimentary beds exposed in the mountains of the Desert region are of Paleozoic age, and many crystalline schists appear, while the sedimentary beds exposed in the valleys are Post-Tertiary. The crystalline schists and ancient sedimentaries of the mountains are often extensive masses of extravasated rocks. The prevailing type of orographic structure is that of monoclinal ridges of displacement. Blocks of strata have been turned up so as to incline at various angles, and from their upturned edges the mountains have been carved. But these monoclinal ridges are much complicated by mountain masses having an eruptive origin.
In the eastern districts the materials denuded from the mountains and plateaus have been carried to the sea, but in the western districts the materials carried from the mountains are deposited in the adjacent valleys, so that while the mountains are composed of rocks of great age, the rocks of the valleys are of recent origin. In that geological era known as the Glacial epoch the waters of a great lake spread over these valleys, and the mountains stood as islands in the midst of a fresh-water sea. For the history of this lake we are indebted to the researches of Mr. Gilbert. It had its outlet to the north by way of the Shoshoni River and the Columbia to the North Pacific. These later beds of the valleys are in part the sediments of Lake Bonneville, the great lake above mentioned, and in part they are subaërial gravels and sands.