68 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
doubtedly had a radial course from off the mountain dome. Now 
the drainage through the gap is in the opposite direction. A little 
stream, working on the face of the escarpment, has appropriated the 
gap and has cut back sufficiently to divert the headwaters of a small 
stream in the Red valley and to lead them by a shorter course through 
the gap into Whitewood Creek, while the beheaded portion continues 
on its longer, gentler course outside the escarpment and joins the same 
stream two miles below. 
PRESENT STREAM Courses. In Boulder valley the present stream 
courses bear little relation to the broad, ancient excavation, which 
they partly occupy. Insignificant streams flow both east and west 
from a divide established near the west end of the main gravel deposit. 
They are busily engaged in dissecting the terraces and entrenching 
themselves in the firmer rock beneath. 
Elsewhere in the distriet the stream courses are in the main well 
adjusted to structures and notably follow the strike of the rocks. 
Whitewood and Bear Butte Creeks, the two master streams of the 
region, give clear evidence of superposition from superior strata since 
removed. Just below the town of Crook, Whitewood Creek cuts 
across a pinched anticline, not at its lowest point but nearly half a mile 
southeast of it, thereby severing the shoulder of the anticline from. the 
main mass. Four miles farther southeast, Bear Butte Creek cuts 
through the same arch in a splendid gorge, five hundred feet deep, on 
the sides of which the anticlinal structure appears with almost the 
symmetry and beauty of a rainbow. None of the streams above 
noted have yet graded their valleys, though in some instances graded 
reaches have been established. 
SUMMARY OF FIELD EVIDENCE. An ancient stream, with possible 
tributaries from the west and south, flowed in a general east-northeast 
direction through Boulder valley with a slope of seventy or eighty 
feet per mile. Its sources were in the Terry Peak region and its 
drainage basin was probably equal to those of Whitewood and Bear 
Butte Creeks combined. There is good evidence that the predecessor 
of Bear Butte Creek joined the main stream, as a tributary, at Boulder 
Park and that it was later diverted northeastward by capture. If, 
however, such capture took place, it must have occurred previous to 
the conditions which permitted the incision of the present gorges; 
for Bear Butte Creek has been superposed on the anticline east of 
Boulder Park and now cuts through it in a fine gorge. The depth of 
the gorge, five hundred feet, is considerably greater than that of 
the later portion of Whitewood canyon, two hundred and fifty feet, 
