The physical geography of the region drained by the waters of the river is highly interesting, and has an important relation to the subject. The area in question consists of a series of tabular blocks, of vast proportions, cut out of the general platform of the country by great faults, and lifted above it from 2,000 to nearly 6,000 feet, so that the absolute altitudes (above sea level) of the tables range from 9,000 to 11,500 feet. Where the valleys are lowest the tables are highest, and _vice versa_. The valleys or lowlands stand from 5,000 to 7,500 feet above the sea. The plateaus have areas ranging from 400 to 1,800 square miles, and collectively with the included lowlands within the drainage system of the Sevier have an area of about 5,400 square miles. The tables front the valleys with barriers which are more continuous and which more closely resemble long lines of cliffs than the mountain chains and sierras of other portions of the Rocky Mountain Region, and there are stretches of unbroken walls, crowned with vast precipices, 10, 20, and even 40 miles in length, which look down from snowy altitudes upon the broad and almost torrid expanses below. If the palisades of the Hudson had ten times their present altitude and five or six times their present length, and if they had been battered, notched, and crumbled by an unequal erosion, they would offer much the same appearance as that presented by the wall of the Sevier Plateau which fronts the main valley of the Sevier. If they were from six to eight times multiplied, and extended from Hoboken to West Point, and were similarly shattered, they would present the appearance of the eastern wall of Grass Valley. If they were eight to ten times multiplied, and imagined to extend around three-fourths of the periphery of an area 40 miles by 20, and but little damaged by erosion, they would represent the solemn battlements of the Aquarius Plateau. These great plateaus are masses of volcanic rock overlying sedimentaries, the latter so deeply buried that they are seldom seen even in the deepest chasms, while superposed floods of volcanic outflows are shown in sections, reaching sometimes a thickness of 5,000 feet. The dark colors of these rocks give a somber aspect to the scenery, and the gloomy fronts of the towering precipices are rendered peculiarly grand and imposing.