102 JOSEPH P. ID DINGS 



are definitely located on fault lines, there are the channels of 

 Bear Gulch and Crevice Gulch, Hell Roaring and Slough Creeks, 

 with tributaries to Boulder River and Mill Creek, and the upper 

 portion of the West Boulder. 



Another conjugate system of fractures is indicated by the rect- 

 angular drainage with lines almost north-south and east-west. 

 The direction of the main Boulder River through its canyon is the 

 same as that of several of its head branches, of Buffalo Creek to 

 the south, and of several north- south drainages to the east. 

 The east-west direction is found in tributaries of the Boulder 

 River, in the North Fork of Mill Creek, and in a stream in line 

 with this east of East Boulder plateau. In this case there is a 

 fault nearly parallel to the North Fork of Mill Creek connected 

 with the northwest-southeast system of faults. An east-west 

 fault has also been observed by Mr. W. H. Emmons near Hay- 

 stack Peak at the head of Boulder River. There can be little 

 doubt that in this portion of the quadrangle there is a system of 

 fractures in an east-west and north-south direction. 



The sculpturing of the canyons of the Boulder and West 

 Boulder, and of several to the east, seems to require the action 

 of other agencies than those of ordinary erosion. These narrow 

 canyons have been cut 3,000, 4,000, and 5,000 feet into gneiss 

 and schist within a few miles of their heads, and their drainage 

 basins seem quite inadequate to furnish sufficient water for so 

 great and such deep erosion. It seems as though the rocks must 

 have been rendered more susceptible to abrasion by being fract- 

 ured or jointed. 



A similarly placed system of drainage channels exists in the 

 northwestern corner of the quadrangle west of Shields River 

 and east and south of the Bridger Range, but no system of fract- 

 ures or faults has been noted in this region. 



The northeastern corner of the quadrangle is intersected by a 

 distinctly rectangular system of drainage. The channels of the 

 Yellowstone and Boulder Rivers, with the tributaries of the 

 Shields River, have a northern trend nearly at right angles to 

 those of Shields River and several creeks flowing southeast 

 from the Crazy Mountains, and numerous small tributaries of the 



