THE GLACIAL GEOLOGY OF GRAND 

 MESA, COLORADO 



JUNIUS HENDERSON 

 University of Colorado 



The great number of lakes reported on and about Grand Mesa, 

 Mesa County, Colorado, has long suggested glaciation to the writer, 

 notwithstanding the fact that the mesa, which includes several 

 townships, rises but little over 11,000 feet above sea-level and 

 does not extend above timber line. However, I have never found 

 any reference to glaciation in the hterature of the region. In 

 company with Mr. John P. Byram, of Mesa, Colorado, two weeks 

 were spent on the mesa in August, 1923, with saddle and pack 

 horses, accompanied for one day by Mr. Erwine Stewart, also 

 of Mesa, who had told us of phenomena indicating glaciation. 

 The evidence of intense glaciation is everywhere abundant around 

 the north and east sides, and on a considerable part of the top, 

 presenting two distinct types that I have not yet seen elsewhere 

 in Colorado. 



The ancient glaciers of Colorado, though confined to the moun- 

 tainous portion, covered, at their greatest expansion, over 10 per 

 cent of the total area of the state. Most of them originated along 

 the crests of the higher mountain ranges above the 11,000 foot 

 contour, and extended down deep, pre-existent gulches as typical 

 mountain- valley glaciers ranging from three to sixty miles in length. 

 Definite, well-marked cirques occupy the heads of these gulches, 

 well above the present timber line. But in contrast with the com- 

 mon type of glaciation in the Rocky Mountains, deep gulches 

 are absent from Grand Mesa, and cirques, if present at all, are 

 so vague and ill-defined as to be scarcely recognizable. 



Grand Mesa is bounded on all sides by a precipitous escarpment 

 of basalt, a very important factor in the glacial geology of the 

 region. The highest point determined by us by aneroid barometer 



676 



