russell.] MOUNTAINS. 15 
almost vertical, while the west slope, from 20 to 30 miles in length, 
has an inclination varying from about 3° at the crest line of the 
mountain to less than 1° at a distance of 15 miles, and continuing to 
decrease still farther westward. Southwest of the highest portion of 
the uplift the rocks of which it is composed are bent into a broad, 
gentle syncline that widens out to the northwest and passes beneath 
Harney and Malheur lakes. The longer axis of this synclinal trough 
pitches to the northwest and the inclined basin produced by the 
faulting and folding is drained by Donner and Blitzen River. 
Stein Mountain is thus a typical monoclinal block of large size. 
The entire length of the uplift is in the neighborhood of 100 miles, 
but its extremities have not been closely examined. It is apparent 
that the main part of the eastward-facing cliff, forming the highest 
portion of the uplift for a distance of over 20 miles, is a fault scarp, 
along the base of which recent movements have taken place, as is 
indicated by the occurrence of hot springs and fresh breaks in alluvial 
deposits. During a visit to this region in 1882 a I believed this fault 
to continue far to the north, but more detailed study must be made 
before this can be considered as fully established. It may be that at 
the north the Stein Mountain fault scarp merges with a similar 
eastward-facing cliff, which may be interpreted as being due to the 
erosion of an anticline. To the east of the great line of cliffs referred 
to there are other monoclinal ridges, which, so far as the evidence 
now iii hand is concerned, may be interpreted as remnants of a deeply 
eroded anticline, instead of evidence of extensive faulting, as pre- 
viously considered. 
The rocks of which Stein Mountain is composed are principally 
basalt, in well-defined sheets. The basalt, as is well known, was 
poured out in a molten condition, either from fissures, forming what 
are termed massive eruptions, or, what is more probable, from well- 
defined volcanic vents, as has happened in many instances in the same 
general region in recent times. The age of the Stein Mountain basalt 
is probable Middle Tertiary, and it seems to be a part of the great suc- 
cession of widely extended lava flows, termed in a general way the 
Columbia River lava. In the highest and grandest portion of the 
mountain the layers of basalt are in many instances separated one from 
another by layers of coarse yellowish sandstone, varying in thickness 
from 4 or 5 to about 15 feet. In one section, obtained while climbing 
the east face of the uplift, which overlooks Alvord Desert, seventeen 
of the sheets of sandstone referred to were observed. The basaltic 
layers average perhaps 60 to 75 feet in thickness, and a large number 
are present. The entire thickness of the great pile of widely extended 
sheets of basalt is about 5,000 feet. 
On the west side of Alvord Desert, and for a distance of about 10 
a Russell, I. C, A geological reconnaissance In southern Oregon: Fourth Ann. Rept. U. S, 
Cteol. Survey, 1884, pp. 431-461. 
