MANSFIELD: POST-PLEISTOCENE DRAINAGE. 67 
Stream Engows. Bear Butte Creek —Boulder Park. At the point 
where. Bear Butte Creek enters Boulder Park it makes a rectangular 
bend northeastward, turning from a course across the strike of the 
rocks to one that follows the structure closely. The two patches 
of gravel just east of the bend have an elevation consistent with that 
of the main gravel body. 
Boulder Park — Crook Valley. At the northern part of Boulder 
Park the main gravel body makes the eastward inclination already 
noted and points toward the wide gap in the outer hog-back ridge, 
now occupied by Spring Creek. The stream, which now drains 
Crook valley, is excavated in the weak strata of the Red Beds, which 
are here folded into a narrow syncline, and makes nearly a right angle 
with the direction just indicated. Moreover the gravel patches in 
Crook valley are fifty to one hundred feet lower than the elevation of 
the main body at the head of the valley. Here the evidence corro- 
borates that already cited and points to the former continuation of the 
main stream through Spring Creek Gap and its later diversion north- 
ward through Crook valley. 
Whitewood Creek. (a) The continuation of the high-level White- 
wood valley beyond the west end of the gravel terrace has already 
been noted. The course of that valley makes a large angle with that 
of the ancient stream as shown by its gravel deposits. 
(b). Three and a half miles below Deadwood, Whitewood Creek 
makes a rectangular turn eastward; but the high-level valley continues 
on for half a mile and ends at a saddle in the divide, which overlooks 
the Red valley and has been tunneled by the railroad in its escape 
from the gorge. The direction of the valley, however, is continued 
by an insignificant stream which drains into the Red valley. Just 
below the bend occur the two patches of gravel at locality 16 and across 
the canyon (Plate 1). 
Sandy Creek. Sandy Creek joins Whitewood Creek at a rectangular 
bend a mile and a half west of Crook Mountain. The eastern limb 
of the bend continues the valley of Sandy Creek northwestward for 
nearly a mile. There the stream turns abruptly northeastward again; 
but a broad high-level wind gap occurs on the west side of the gorge, 
two hundred feet above the present creek, and beyond, in the same 
northwesterly direction, a small stream flows into the Red valley. 
Spiegel’s Gap. On the northwest flank of Crook Mountain there 
is a beautifully symmetrical V-shaped gateway, in the Minnekahta 
limestone, the arms of which rise in an escarpment four hundred feet 
above the level of Whitewood Creek. The stream that carved it un- 
