110 
SNAKE RIVEK PLAINS OF IDAHO. 
[bull. 199. 
northeast slope, and possibly a summit overflow of liquid lava did 
occur, but the subsequent downwashing of lapilli has concealed the 
evidence in this connection which may formerly have been present. 
From the summit of Kuna Butte four other similar but smaller 
conical elevations may be seen on the plain to the southwest, at dis- 
tances of 4 to perhaps 10 miles. These appear to be cinder cones 
marking the sites of once active volcanoes. 
Crater rings near Cleft. — Three miles south of Cleft, and. as indi- 
cated on the map forming tig. 1, at the top of a broad, low elevation 
Fig. 1.— Map of crater rings near Cleft. Scale, 1 inch = 2 miles; contour interval, 50 feet. Dotted 
lines indicate stream channels; figures give elevation above the sea. 
on the featureless plain, there are two circular depressions with verti- 
cal inclosing walls, but without elevated rims. These pits are evidently 
to be classed as crater rings/' which are generally considered by 
geologists to owe their origin to volcanic explosions. 
Each of these rings has a level floor composed of fine yellowish soil, 
like that covering the adjacent plains, and no crags or solid rock of 
any kind occur within them. 
The smaller of the two pits, situated to the west of its companion, 
has a diameter, measured across its level floor, of about 800 feet. The 
inclosing cliffs, with conspicuous talus slopes, are 200 feet high, and 
present the appearance of the wall of a canyon cut in horizontally 
bedded sheets of massive and, in part, columnar basalt. The summit 
of the wall of the depression is surrounded, to use an expressive term 
current m the Far West, by a "rim rock" of black lava. Some ofi 
« J. W. Judd, Volcanoes. New York, 1881, pp. 170-17( 
