PHYSICAL ASPECT OF THE GPtEAT PLAINS. 3 



From Cheyenne westward, the grade becomes much more rapid, and 

 between that town and Granite Canon, which hes well np on the mountains 

 on the Archaean rocks, a distance in a direct line of 18 miles, we have a 

 rise of 70 feet to the mile; this, however, can hardly be regarded as giving 

 the correct slope of the plains, owing to the position of Granite Cailon, 

 which lies several hundred feet above what, in the other measurements, 

 was considered the base of the range. 



In a north and south line, the rise and fall in elevation is nearly as 

 great, but is at the same time so gradual, and the configuration of the 

 country such, that the nature of the slope is by no means so well recognized. 

 Between Crow Creek and Horse Creek, about 30 miles to the northward, 

 on the meridian of Cheyenne the plains have an average altitude of nearly 

 6,000 feet above sea-level, but fall off steadily in both directions. To 

 the southward from Cheyenne the country slopes off, until at Evans near 

 the lower boundary of the map, a distance of 52 miles in a direct line, 

 the height above the sea is only 4,745 feet, a descent of 1,330 feet, or over 

 25 feet per mile. North of Horse Creek, the slope is steadily to the north- 

 ward, the descent being nearly 1,000 feet to the North Platte River, a few 

 miles beyond the upper limit of our map. 



Numerous streams from the mountains between the Laramie River and 

 the Big Thompson Creek, reaching ultimately the North Platte or South 

 Platte River, cross the plains within the belt of our survey; but few of 

 them, however, are of any considerable size. Along the elevated plateau 

 ah-eady mentioned, the streams have a general east and west course, while 

 to the north of Horse Creek and south of Crow Creek, conforming to the 

 general configuration of the country, they run either northeast or southeast. 

 These streams have cut for themselves, through the loose, friable sandstone 

 formation, broad valleys of great uniformity of character and monotony of 

 aspect, frequently 4 and 5 miles in width, but rarely depressed more than 

 100 or 200 feet below the general surface, although hemmed in by precipi- 

 tous walls, sometimes several miles in length, without any marked break in 

 their cliffs. 



Although the Great Plains present but few striking physical features, 

 in the detailed outlines they^ show great variety of form in the rounded 



