186 GUIDEBOOK OF THE WESTERN UNITED STATES. 



dips only slightly toward the north, and as it has ,a thickness of 

 about 3,000 feet, the valley which it occupies and which has been 

 formed by its erosion is of considerable width. To the north the 

 rocks above the Mancos shale cap the Book Cliffs, which were so 

 named because the beds of rock when seen from a distance suggest 

 the edge of a book lying on its side. To the south the underlying 

 variegated sandstone of the Gunnison formation makes the slope 

 that leads up to the gi-eat red cliffs on the Uncompahgre Plateau. 

 The traveler may see these rocks, as already stated, soon after leav- 

 ing the station at Grand Junction, and they ,are generally in sight 

 on both sides of the road as far as Mack. 



The peculiar shape and structure of the Book Cliffs (see PI. 

 LXVIll, p. 157) gives them a striking resemblance to architectural 

 features. In their lower part they are composed of shale, which is 

 capped by heavy beds of sandstone that lie almost flat. Nearly 1,000 

 feet of shale is exposed, and where it is not protected by blocks of 

 sandstone that have fallen from the ledges above it has been cut by 

 the rain into innumerable branching ravines separated by low ridges. 

 Viewed from a distance when the sun is low enough to cast a shadow 

 on one side of these dividing ridges the sculpture is marvelously 

 accurate and sharply defined, resembling the venation of a leaf. 

 The slope is steep, nearly 45°, and the profile of the slope and the 

 cliff above is well shown in Plate LXVIII (p. 157) . 



The cliffs on the south are composed of great beds of red sandstone 

 or white sandstone stained red by the overlying shale. At first sight 

 these beds appear to lie so nearly flat that if they were extended 

 they would reach entirely across the river vallc}^ and would lie far 

 above the head of the traveler. TMien they are studied closely, how- 

 ever, they may be seen to bend down sharply as they approach the 

 river, and in reality they pass under the stream instead of far above 

 it. The bend in the rocks may be seen by looking back after the 

 train has gone a mile or so beyond the station. 



In this valley, as in most other irrigated parts of the "West, the 

 railroad does not traverse the area that is most highly cultivated, 

 and the traveler may think that a large part of the valley below 

 Grand Junction consists of land so highly impregnated with alkali 

 ^ as to be unfit for farming, but here and there he may catch a glimpse 

 of the terrace or bench lands, which support the finest ranches in 

 the valley. Along the railroad he may see some good ranches and 

 orchards, and in striking contrast to them he may see in many places 

 remnants of the original growth of sagebrush which covered the 

 whole valley before it was irrigated and cultivated. This valley 

 is the most arid part of Colorado, for, according to the records of 

 the Weather Bureau, its annual rainfall is only 7.7 inches. The 



