7() SNAKE RIVER PLAINS OF IDAHO. [bill. 199. 
border of the Snake River Plains and approximately 1,000 feet higher 
than their present surface. The lava descended a slope which rises 
from the plain with an estimated gradient of about 200 feet to the 
mile, and on leaving the mountains spread far and wide on the adja- 
cent plains. The sheet of lava thus formed reached the site of Snake 
River and appears as a rim rock in the bluffs at Glenns Ferry. In 
the mountains the lava stream cooled with a rough surface, but on the 
plain became quite smooth. Its surface is no longer fresh in appear- 
ance, and where not covered with soil it is much broken and a sheet of 
loose, weathered stones and bowlders, with dark soil in the crevices, has 
been formed. That this lava is of comparatively ancient date is shown 
also by the amount of work that has been accomplished by the creek 
that flowed over it. Little Canyon Creek, although now dry during the 
summer season, and thus evidently a weak stream, has excavated a 
remarkably rugged canyon in the basalt and underlying rhyolite to 
a depth of 200 feet where it leaves the mountains. The lava sheet cut 
through is compact, and at the locality just referred to is about 50 
feet thick and nearly a mile broad. 
KINO HILL LAVA STREAM. 
In the region drained by King Hill Creek (the next creek east of 
Little Caivyon Creek), as was observed from a distance, there is a large 
lava flow, which descended the mountains at about the same time the 
Little Canyon flow occurred, and spread widely on the plain to the 
south. The appearance of a remnant of this lava sheet, left as an 
outstanding butte by the erosion of King Hill Creek, is shown on 
PL VIII, .1. 
BLANCHE CRATER. 
In the canyon of Clover Creek, about 1 mile south of Blanche post- 
office, there is a black cone which rises about 60 feet above the adjacent 
flood plains of Clover Creek and has a perfect crater in its summit, 
The conical pile is composed principally of thin cakes of highly vesicu- 
lar black lava, some of which are strewn about on the surrounding 
stream-formed sediments and were evidently blown out by the vol- 
cano in a highly plastic or actually liquid condition. Within the 
relatively large conical depression in the summit of the volcanic 
pile there is a shallow lake of intensely alkaline water, which is sup- 
plied by small, warm springs. The concentration of the water by 
evaporation has led to the precipitation of alkaline salts mingled with 
organic matter. Forming the shores of the lake and underlying it 
there is a bed of alkaline salts having an average depth, as reported 
by Mr. B. C. Brey, who owns a neighboring ranch, of about 15 feet, 
and an area of 3 acres. This deposit has been utilized in a small way 
in the manufacture of soap. From the base of the crater a small 
