392 WALLACE W. ATWOOD AND KIRTLEY F. MATHER 
it contains great quantities of bowlders of pre-Cambrian rocks— 
quartzites, schists, gneisses, and granites—which must have been 
obtained from near the headwaters of the Rio Grande. The débris 
Uinta outwash 
Uinta moraine 
i PATTER 
( Bighorn outwash 
’) Bighorn moraine 
if 
\ 
i) ES 
x 
a 
Modified 
Bighorn moraine 
San Juan moraine 
Limits of glaciation 
Uinta ee 
Bighorn -e—e—e= 
San Juan ~-o-—o 
Map of the upper Piedra River 
Topography from San Cristobal quadrangle and Hayden Atlas- 
0 vol 2 23) 4 5 Miles 
i 
Contour interval 500 feet 
Fic..2 
transported by the tributary glaciers from the south is largely of 
volcanic origin. 
The third largest glacier of the region during this epoch was 
that in the Uncompahgre Valley on the north side of the range. 
