348 



E. B. BRANSON BULL LAKE CREEK ROCK SLIDE 



sissippian), 76 feet tliick, comes in above the Madison, forming a terrace, 

 and finally the Tenslee]) (I\Minsyl\anian) adds a 400 to (500 foot cliff 

 above the Amsden. 



Description of the Bull Lake Cueek Slide 



On the broad, steejdy slo])inc>' terrace extending from the base of the 

 northern wall of the outer canyon to the rim of the inner gorge is a rock 

 slide, or rock glacier, about 5 miles long and one-half to one mile wide. 

 Starting at the west end of the north cliff the rock slide moves down a 

 lO-degree slope along the cliff' base for 4 or 5 miles, then turns almost at 

 right angles, crosses a terrace less than a mile in width, and enters the 

 granite gorge. 



The slide is made up of rock fragments varying from mud particles to 

 blocks of limestone 40 feet in diameter, and the large and small frag- 

 ments are mixed together in endless variety. The largest blocks are of 



P'lOi'UE 1. — Lo/'-rr End of Bull Lake Creek m.ide 

 Photograph was taken neni- nunioral 1', plate 21, figure 1, hy Warner 



Bighorn dolomite, l)ut the greater part of the debris comes from the 

 Shoshoni limestone. A series of longitudinal ridges traverses most of 

 the slide and these are interrupted by many cross-ridges. Eidges made 

 of fine material sometimes have one side 20 feet high, with a slope of 40 

 to 50 degrees. Cross-ridges covered with very large blocks of rock have 

 separated, leaving deep valleys between, with black, shaly mud exposed 

 at the bottom. On the sides there are ridges reseml)ling the lateral mo- 

 raines of glaciers and at the upper end an amphitheater-like depression 

 resembles a cirque. 



