PLEISTOCENE HISTORY OF SAN JUAN MOUNTAINS 395 
dome. Further physiographic studies in the range will probably 
yield conclusive data on this problem. 
The Bighorn glacial epoch.—Beyond the limits reached by the 
Uinta ice at its maximum extent there are, in each of the valleys 
noted above, deposits of glacial drift which prove the presence in 
these valleys of ice of an earlier epoch. These drift deposits are, 
in most cases, remnants of the terminal moraines of the next 
earlier, or Bighorn, glaciers and are found from one to three miles 
downstream from the Uinta terminal moraines. ‘The greater size 
of the Bighorn glaciers is also evidenced in some of the valleys by 
the presence of remnants of lateral moraines on valley slopes at 
greater elevations than those of the Uinta epoch at those localities. 
The remnants of the terminal moraines deposited by the Bighorn 
ice are in each case situated on rock benches which vary in elevation 
up to something more than 300 feet above the present stream 
channels. This relationship is well shown in the Animas Valley 
where the Bighorn moraine is found on the very prominent rock 
bench east of the city of Durango and at an elevation of more than 
300 feet above the present valley bottom. The northern portion 
of this rock terrace is heavily mantled with the morainal débris, 
while downstream from the front of the moraine the terrace is 
capped with outwash gravels having in places a thickness of at 
least thirty feet. In each of the main canyons east of the Animas 
similar conditions obtain. 
At the time of the advance of the Bighorn ice Huerto Creek 
(see Fig. 2) was tributary to the Weminuche through the low sag, 
now partially filled with Uinta drift, just south of the San Cristobal 
quadrangle, and the ice in the two valleys, coalescing at this point, 
moved down Weminuche Creek a distance of three miles below the 
lower limits of the Uinta drift in that valley. Remnants of the 
terminal moraine deposits at this point are found on a rock bench 
75 feet above the present stream. The small amount of post- 
Bighorn Valley cutting here as compared with that in the Animas 
Valley is probably due to several causes. The diversion of the head- 
waters of Huerto Creek, which will be accounted for later, robbed 
the Weminuche of nearly half of its former volume; the Animas is 
a very much larger stream than the Weminuche and is capable of 
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