THE A WAP A PLATEAU. 273 



masses constituting the High Plateaus. The slopes of the entire mass all 

 converge towards a central depression called Rabbit Valley. It is not an 

 inclined plane or roof, but the segment of a dish. Everywhere the general 

 inclination is very slight, though undulating with low hills. The western 

 boundary is a wall from 1,800 to 3,0U0 feet high, plunging down into Grass 

 Valley, sometimes by a grand precipice, sometimes by a steep, difficult 

 slope and always abruptly. The length of the plateau, though its bound- 

 aries are for the most part difficult to locate with precision, is about 35 

 miles and its breadth about 18 miles. 



It is a dreary place. Upon its broad expanse scarcely a tree lifts its 

 welcome green, save a few gnarled and twisted cedars. Its herbage con- 

 sists only of the ubiquitous artemisia and long nodding grasses. Not a spring 

 or stream of water is known upon all its area, except at the lowest part, where 

 its slope merges into the floor of Rabbit Valley. And yet most of its sur- 

 face is at an altitude where verdure and moisture abound, and where the 

 summer is like the spring of more favored regions. But here the snows of 

 winter are melted early, and the summers are nearly as hot and drv as those 

 of the plains below. A ride across it is toilsome and monotonous in the 

 extreme. It takes us over an endless succession of hills and valleys, clad 

 with a stony soil, usually just steep enough to worry the animals, but not 

 enough so to require us, or to even encourage us, to dismount. Here 

 and there a sharp canon opens across the path in an unexpected manner, 

 compelling a long detour to find a crossing. These are usually shallow, 

 rarely exceeding 400 or 500 feet in depth, but are as typical in their forms 

 or sections as the canons in the sedimentary strata. 



The whole mass of the Awapa consists of volcanic materials. The 

 only localities where sedimentary beds are seen are in Rabbit Valley and 

 low down in the western flank opposite East Fork Canon in Grass Valley. 

 In the latter locality the great fault has brought them to daylight, and 

 the ravines have still further opened them to view. They are Lower Ter- 

 tiary, corresponding to the Bitter Creek beds of the northern plateaus. 

 Above them are 3,000 feet of volcanic conglomerates and lavas. In Rab- 

 bit Valley beds presumed to be of the same age are also discovered 



beneath thin cappings of trachyte and basalt. Hence it appears that the 

 18 H p 



