50 
GEOLOGICAL REPORT-THIRTY-FIFTH PARALLEL. 
Camp 125, and below Camp 126 the lava formed the summit of perpendicular cliffs on both 
sides of the river, ranging from two hundred to four hundred feet in height. The base of the 
cliffs is formed of red argillaceous sandstone, and above it of red conglomerate. The narrowest 
part of this canon is about four hundred yards wide. Mr. Marcou also noticed gneiss and 
talcose schist. A wood engraving representing this canon is given by Captain Whipple, page 
108. According to Mr. Campbell, this lava extends on the south bank of the river as far 
as the Great Colorado, and even beyond it, on the opposite side, for a long distance. The strata 
which are thus overlaid by lava are probably identical in age with those of a similar nature 
seen higher up the -river, which Mr. Marcou considered Tertiary. 
LAVA BLUFFS ON THE HAWILHAMOOK. 
The bluffs represented in the above sketch are on the south side of the Hawilhamook, at Camp 
126. They rise from eight hundred to one thousand feet above the stream. The base of the 
bluff consists of strata of red sandstone and conglomerate, but the upper and thickest layer is of 
basaltic lava. The sketch indicates that this rocky roof, or covering for the softer strata below, 
is itself liable to rapid decomposition and degradation by the weather. 
Valley of the Colorado river and mouth of the Hawilhamook , or Bill Williams' fork. —Beyond 
the narrow canon in the basalt, the strata of red sandstone and conglomerate are continuous, 
with occasional interruptions to the mouth of the river. Near this point they were upraised, 
and dipped westward at an angle of twenty degrees. They occur again between Camps 128 and 
129, on the western bank of the Colorado river, where they also dip to the west at the same 
angle. Mr. Marcou also mentions vast hills of drift. This is very probably detritus from the 
surrounding mountains. 
The valley of the Colorado is narrow, and hemmed in on both sides by rugged granitic mount¬ 
ains, which are parallel with the Aquarius and Cerbat ranges. The prevailing trend is north 
