GRAVEL AS A RESISTANT ROCK 499 



tains which supplied the material for its construction. Nor is this 

 lowland the site of a stream valley. It runs, on the contrary, 

 parallel to the strike of the beds and is crossed directly by the 

 course of all the streams which flow from the mountains out through 

 the dissected plateau to the desert beyond. 



A good idea of the nature of the lowland may be gained from the 

 photograph, Fig. 3 (see also the map, Fig. 1). This shows the low- 

 land in the foreground and to the left; the even-topped gravel 

 plateau on the skyline; and, sloping down toward the observer, 



Fig. 3. — Looking southeast from the Central road three miles east of Silver City. 

 This view shows clearly the even-topped gravel plateau and its inward slope toward the 

 lowland in the foreground. 



the inner scarp of the plateau facing the lowland at the divides 

 between streams. The view is looking southeast from the Central 

 road three miles east of Silver City. 



On the interstream ridges the difference in elevation between 

 the inner lowland and .the tops of the plateau surface varies between 

 50 and 100 ft. In going northward along the tops of the divides, 

 toward the mountains, one must travel from ^ to 2 miles before he 

 again encounters ground as high as the tops of the gravel plateau. 

 If the dip slope of the plateau surface is projected across the low- 

 land toward the mountains the present land surface is not inter- 

 sected within a distance of about 4 miles, on the average, from the 



