PLEISTOCENE HISTORY OF SAN JUAN MOUNTAINS 301 
The largest of the glaciers of this epoch was that which occupied 
the Animas Valley on the south slope of the range. The gathering 
grounds for this glacier covered several hundred square miles and 
it had a length of over fifty miles. ‘The terminal moraine deposited 
when this glacier was at its maximum extent is near Animas City, 
two miles north of Durango. This moraine consists of two well- 
marked ridges swinging across the valley floor in broadly crescentic 
lines. Downstream from the Animas City moraine there are 
outwash deposits which extend for many miles. Upon one of the 
terrace remnants of this outwash is situated the city of Durango. 
Two slightly different levels appear to have been capped with 
outwash materials at this time and the uppermost of the two is less 
than fifty feet above the present stream channel. 
Similar but smaller glaciers occupied the valleys of the Florida, 
Vallecito, and Pine rivers, situated east of the Animas. The 
terminal deposit of the Florida glacier is in the form of a number of 
low hills or knolls scattered over the valley floor, while the ice in 
the other two valleys coalesced and the terminal deposit crosses the 
valley flat of the Pine River a mile below the junction of the two 
streams. 
Still farther east the four large streams which together form the 
Piedra River show the results of ice occupancy during the Uinta 
epoch. The terminal deposits in these valleys are likewise well 
within the foothill zone and, as shown in Fig. 2, are limited to the 
immediate valley flats. The streams have cut but narrow channels 
through these morainal barriers. 
Another glacier of considerable size occupied the valley of the 
Rio Grande, extending from well within the Silverton quadrangle 
to the eastern margin of the San Cristobal quadrangle. South and 
southeast from Bristol Head at the lower ends of Middle Creek, 
Trout Creek, and South River (see Fig. 3) there is a very con- 
siderable mass of morainic material deposited from the glaciers 
which, during Uinta times, filled the four valleys mentioned and 
united in the Rio Grande Valley. This deposit has a typical 
morainal topography and must aggregate a thickness of 200 to 300 
feet in places. Near the middle of the Rio Grande Valley, the 
material is almost entirely that left by the Rio Grande glacier and 
