26 
GEOLOGY—CHICO CREEK TO FORT READING, 
still bare, and exhibiting all the waves and eddies of a flowing stream. Some of these trappean 
rocks were apparently older. Among them were porphyry, trachyte, and volcanic breccia, in 
which the imbedded fragments formed masses of several hundred pounds weight. No drift 
action has modified the surface of these rocks ; hut, with the exception of the marks of 
atmospheric weathering, which they exhibit in different degrees, they are as rough, and their 
surfaces as fresh, as though but recently formed. The thin soil which covers or surrounds them 
is derived only from their decomposition, and is often highly colored by oxide of iron. It 
seems to possess the inorganic elements of fertility, and sustains among the rocks a vigorous 
growth of wild oat. 
On the north side of Bear creek valley is a more striking proof of the comparatively recent 
date of volcanic action in this vicinity than even the lava streams. This is furnished by a vol¬ 
canic cone 500 or 000 feet in height, which has a crater on the summit, and of which the sides 
are covered with reddish scoria. 
VOLCANIC CONE NEAR FORT READING. 
On Bear creek black obsidian occurs in considerable quantities, and some of it was brought 
me, as “probably some kind of stone coal.” 
The trap ranges in this vicinity, of which I have spoken, form high and sometimes preci¬ 
pitous banks to the Sacramento river, with but little level land between them, and consti¬ 
tute the entrance to the almost continuous canon through which it flows for nearly a hundred 
miles. 
