DAVIS: MOUNTAIN RANGES OF THE GREAT BASIN. 167 
before dying out. The frontal escarpment of the monocline is very 
straight and but little dissected ; the fans at its base are low, and a 
very gentle slope of alluvium leads from the base line to a dead level 
playa, half a mile to the east. The lava monocline is somewhat compli- 
cated by a transverse fault and a transverse monoclinal fold; but the 
frontal escarpment pays no attention to these disturbances. 
The Stein mountains, Figure 14, continue the general line of the Pueblo 
mountains, although separated from them by the westward re-entrant 
already mentioned. The structure of this range is, however, unlike that 
of the other in consisting almost wholly of lavas for at least as far as 
some distance north of Andrews. The lavas resemble basalts and ande- 
sites, commonly porphyritic. The range may be conveniently described 
in three parts : the southern part is a warped monocline, dipping south 
and southwest, and obliquely cut off on the east by the north and south 
mountain base; the crest of this part of the range is serrated. The 
middle part is a plateau-like mass, with gentle western dip. The 
northern part is much higher than the rest ; it was generally hidden in 
clouds or haze during my visit, and its structure was not determined. 
I had an excellent view over most of the southern part of the range 
from. the southeast corner of the middle plateau section, whence a great 
extent of country is disclosed. Alvord valley has every appearance of 
being a graben, limited by a fault on the east as well as the west; many 
low ranges trending to the south-southeast are obliquely cut off in a 
notably even line along the eastern valley margin. To the northeast, 
an escarpment bordering the valley is banked up with sands blown from 
the extensive playa of Alvord desert which occupies that part of the 
depression. . 
Not only is the Alvord depression seemingly a trough or graben, but 
the southern and middle parts of the Stein mountains are carved in what 
seems to be a lifted block, with a fault along the western as well as along 
the eastern border. The reason for this opinion cannot be presented as 
conclusive, for it is based only on what was seen from the point of view 
above named, yet there is little doubt in my own mind of its being cor- 
rect. The southern and middle division of the range appeared to be 
evenly cut off along their western border, and this appearance was es- 
pecially distinct for the southern division where the western border 
trends nearly square across a series of monoclinal ridges and valleys. 
The mountain block is ten or twelve miles wide, and is succeeded on the 
the west by a brown-gray plain, at 1,000 or 1,500 feet lower than the 
ridges, and 2,000 or 2,500 feet lower than the middle plateau division. 
