498 JOHN LYON RICH 



While from its nature as a Piedmont accumulation, the gravel 

 of the plateau has not suffered complete elimination of the less 

 resistant elements, it is, nevertheless, an assorted mass in which 

 rocks of the more resistant kinds strongly predominate. A list 

 of a few of the more common of these will give a fair idea of the 

 nature of the gravel and of the extent to which the more resistant 

 rocks dominate. The list follows : green quartzite, white quartzite, 

 light-colored rhyolite, basalt, diorite, epidotized granodiorite, garnet 

 rock, and magnetite from the Hanover ore deposits. 



Fig. 2. — Looking down one of the valleys which crosses the gravel plateau from 

 the lowland to the desert beyond. Note particularly the character of the valley; 

 its narrowness and lack of tributaries. Compare this with the broad valleys developed 

 on the bed-rock of the lowland as shown in Fig. 3. Lone Mountain in the background. 



The coarseness of the material varies. Individual bowlders of 

 large size are buried in a matrix of smaller bowlders, pebbles, and 

 sand. This combination gives a rock of very porous nature, 

 capable of absorbing quickly the water which falls upon it. At the 

 same time the removal of the finer material of the matrix leaves 

 the coarser bowlders and pebbles concentrated at the surface where 

 they form a very effective protective covering — effective against 

 either rain erosion, wind, or decomposition. 



The most conspicuous feature in connection with this plateau 

 is the fact that it is now separated by a lowland from the moun- 



