DAVIS: MOUNTAIN RANGES OF THE GREAT BASIN. 165 
basaltic so far as I saw them, whose westward dip of 15° or 20° is well 
expressed in a series of east-facing escarpments. Paired wet-weather 
subsequent streams drain the longitudinal depression between the two 
ranges, and their gathered waters escape eastward by deep-cut narrow- 
floored, steep-walled gorges through the front range to the broad plain 
known as Alvord valley. Russell marks a fault along the intermediate 
depression (b, 444, Pl. LXXXIV.); but the relation of the western 
lavas to the older rocks of the eastern range, as seen from the Stein 
mountains, Figure 16, from Doane’s ranch near the north end of the 
range, and again in the depression between the ranges back of Deegan’s, 
seemed to be best explained by normal superposition of the lavas on the 
erystal lines, followed by tilting and erosion without faulting. The 
depression between the front and back ranges is thus to be interpreted 
as a series of normal subsequent valleys, eroded along the weaker basal 
members of the lava beds by branches of streams that transect the 
eastern range and that are probably persistent from an earlier pre- 
faulting cycle of erosion. 
The eastern base of the mountains is, however, unquestionably deter- 
mined by a fault on which a-total movement of several thousand feet 
has probably taken place, the latest displacements being of recent date, 
as Russell has shown. The base line of the range is of gentle curvature, 
indifferent to the structure of the mass. An excellent illustration of 
this is seen a mile or more south of Catlow’s ranch, where a boldly out- 
cropping rib of strong rock, standing oblique to the trend of the range, 
terminates evenly with the adjoining weaker rocks at the mountain base, 
and the face of the rib seems much sheared and broken. The ravines 
and gorges through which the range is drained are steep-walled and 
narrow to their mouths. The spurs between the ravines are abruptly 
cut off by the base line, and show no tendency whatever to trail forward 
into the plain. 
Recent faulting along the mountain base is shown by several topo- 
graphic features. At a number of points near the northern end of the 
range, between Catlow’s and Doane’s, open graded valley floors now stand 
a hundred feet or more above the mountain base, and are sharply trenched 
by the streams that formerly graded them. Uplifted and dissected frag- 
ments of broken fans are often seen one hundred feet or more above the 
mouth of a gorge, an excellent example of this kind being found back of 
Denio, while others occur near Catlow’s. In general, the summits and 
higher slopes are of moderate declivity, frequently well covered with 
waste and exposing few ledges; while the walls of the cross-cut gorges 
