ftUSSELL.J 
VOLCANOES. 71 
lava stream extends southward about 1 mile. This stream crossed the 
valley diagonally and formed a dam that checked the flow of Clover 
Creek and caused it to spread out a broad gravel deposit, which is 
now rich meadow land. About a mile north of this interesting crater 
there are copious springs with a temperature of 117° F. 
This crater is one of the latest and possibly the youngest of those 
visited by me in southern Idaho, and is situated in the bottom of a 
canyon about 500 feet deep, excavated in Snake River lava and asso- 
ciated beds of lacustral sediment and lapilli belonging to the Payette 
formation. 
SUMMARY. 
The lava streams which are known to have originated in the moun- 
tains lying north of the Snake River Plains, and which descended to 
them, are, in their order from west to east, the one which descended 
the canyon of the South Fork of Boise River and the Little Canyon, 
the King Hill, Black Butte, and Martin lava streams. These observa- 
tions abundantly confirm the conclusion reached by Lindgren, already 
cited, and expressed in part as follows: a 
The largest flows, however, originated in the foothills north of Glenns Ferry, or 
in fact all along a line extending from Smiths Prairie on the South Fork of the Boise 
to a point northeast of Shoshone. Along this distance of 80 miles the granitic foot- 
hills are completely flooded hy heavy masses of black basalt flows, which extend 
far out into the valley and are here beautifully exposed interbedded with lake beds 
along the canyon of Snake River. 
As previously stated, it is probable that the several craters in the 
neighborhood of Soda Springs furnished similar contributions, which 
reached the Snake River Plains from the southeastward. Lava is also 
reported to occur in the Owyhee Mountains, and it is to be expected 
that other additions to the Snake River Plains from that source will 
be discovered. 
VOLCANOES ON THE SNAKE RIVER PLAINS. 
A critical study of the numerous extinct volcanoes of southern Idaho 
would no doubt show that they may be divided, for convenience, into 
two classes, namely, those which built up cinder and lapilli cones of 
the ordinary type, and those which gave origin to but little fragmental 
material, but formed low, usually flat-topped mounds with immensely 
expanded bases. This classification, while indicating the present con- 
dition of the volcanoes in question, is not strictly logical, as the lava 
mounds were preceded in many and perhaps all instances by cinder 
and lap' Hi cones, which w T ere either destroyed or buried by the great 
effusion of liquid lava which marked the later stages in the eruptions 
of the volcanoes which built them. In fact, a gradation can be found 
" Twentieth Ann. Kept. V. S. Geol. Survey, Pt. III. 1900, pp. 99 100. 
