‚Lower Terrace 
„Shoulder 
Pillar Peak 
Upper Terrace 
BULLETIN: MUSEUM OF COMPARATIVE ZOÖLOGY. 
Fie. 2. Gravel terraces in Boulder Valley. Note the shoulder on the slope of Pillar Peak. 
3) it will be seen that the surface of the 
latter slopes from an elevation of about 
4,750 feet at the west to an elevation of 
about 4,350 feet at the northeast, seventy 
or eighty feet per mile. The altitudes 
thus add confirmatory evidence to that 
furnished by the distribution and sources 
of the gravels, with reference to the direc- 
tion of the trunk stream. Moreover the 
altitudes of the two gravel patches south- 
east of Boulder Park, 4,425 and 4,450 feet 
respectively, are such as to favor the hypo- 
thesis of a tributary stream from the 
south. 
The altitude of the gravel patches 
northeast of Crook Mountain, 4,290 feet, 
suggests that the main stream turned 
northward through the synclinal Crook 
Valley; but the eastward inclination of 
the main body at the head of the valley 
seems to indicate that the earlier course 
of the stream was directly east-northeast 
to the plains. These gravel patches may 
therefore represent a later diversion of 
the stream, by capture, through Crook 
valley. 
The altitude of the gravels at locality 
16 (Plate 1) is nearly three hundred feet 
lower than the surface of the main body 
at its western end. The slope between 
the two places is a little over one hundred 
feet per mile, a considerable steepening of 
the grade over that of the main body in ` 
its east-northeast direction. Here again 
the evidence confirms that already fur- 
nished by the distribution and sources of 
the gravels with reference to the capture 
and northward diversion of the main 
stream. 
TERRACES AND SLOPES. In Boulder 
Creek valley two terrace levels may be 
