150 LANDS OF THE ARID REGION OF THE UNITED STATES. 
south, and from 10 to 20 miles in breadth, called the Sevier Plateau. 
Through this great barrier the stream has cut a wide gorge 4,000 feet in 
depth and 10 miles long, called East Fork Canon, and right at its lower 
end it joins the South Fork of the Sevier. 
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 #,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 Iength, 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 
