398 WALLACE W. ATWOOD AND KIRTLEY F. MATHER 
capped elevations have been noted at many places about the range, 
and in the Ouray quadrangle such gravel cappings have been mapped 
as “‘Earlier Terrace Gravels.’’? 
The mesas slope away from the mountains with gradients of 
150 to 250 feet per mile; their surfaces are from 500 to 1,000 feet 
Uinta outwash 
|} Uinta drift 
YY 
Bighorn outwash} U 
\ q 
| 
4'|] Bighorn drift |} 
San Juan Drift | 
Boulder-mesa |; 
remnants 
Contour interval 500 feet 
Fic. 4.—Glacial deposits at the northwest margin of the San Juan Mountains. 
Topography from the Montrose Quadrangle. 
above the present valley flats, and in each case they are at elevations 
50 to 200 feet above the adjacent terraces which bear the Bighorn 
outwash gravels. Wherever it has been possible as yet to observe 
their relations to remnants of San Juan drift it has been noted that 
* Cross and Howe, U.S. Geol. Survey, Folio 153 (1907). 
eto 
