120 THE DESICCATION OF LATER GEOLOGICAL TIMES. 



favorable. Did, however, such depressions exist on the eastern side of the 

 Rocky Mountains, in the region of the Plains, it is very doubtful whether 

 they could be kept filled with water, since the precipitation is quite small. 



That most elevated belt of the Rocky Mountains comprised within the so- 

 called Parks, beginning at the San Luis Parle, and extending to the Laramie 

 Plains, a region having an altitude of from 8,000 to 10,000 feet, has been 

 more or less occupied by water up to quite a recent period. North Park has 

 already been mentioned in this connection. San Luis Park, however, is 

 much the largest of the comparatively level areas designated by this term. 

 It is about a hundred miles in length, and from twenty to thirty in breadth. 

 Professor Stevenson * considers that this whole area " was at one time occu- 

 jjied by a great fresh-water lake covering an area of several thousand square 

 miles and fed by streams coming from the mountain glaciers." Mr. Endlich,t 

 in describing the same region, quotes Professor Stevenson's remarks, and 

 adds : " Essentially this statement agrees with my own observations." The 

 evidences of terraces seem to be rather obscure ; but the whole aspect of 

 the Park is that of an area covered in large part by water at no very distant 

 period. Mr. Endlich came to the conclusion that there were formerly two 

 large lakes here; one of 1,400, the other of 300 square miles of area. The 

 Rio Grande enters San Luis Park on the west side, and leaves it at the south 

 end, passing through a deep caiion of basaltic lava. Between the former 

 lakes, one of which occupied the northern and the other the southern end of 

 the Park, there is a ma.ss of volcanic rock, through which the river has cut a 

 deep caiion, and Mr. Endlich considers that the water of the two lakes was 

 drained off by the formation of fissures in the lava, which gave the river an 

 unobstructed exit. He also thinks that if the outlet thus produced were now 

 to be closed a new lake would be formed. This supposition must be based 

 on the idea that the Rio Grande drains such an extensive high mountain 

 area that its volume would be more than sufficient to overcome the evapora- 

 tion. This, however, appears to the writer somewhat doubtful, since the 

 streams at present coming into the northern end of the Park from down the 

 slopes of the lofty Sangre de Cristo and Sierra Blanca ranges do not succeed 

 in maintaining themselves against the evaporating tendencies, so as to reach 

 and join the Rio Grande. The upper part of the Park is, in short, an arid, 

 sandy region, but little better than a desert in its aspect. 



* Wheelei-'s Reports, Vol. III., 1875, p. 462. 

 t Hayden's Report for 1875, p. 149. 



