VALLEY OF THE UPPEE YAMPA RIVEE. IQl 



SECTION VIII. 

 VALLEYS OF THE UPPER YAMPA AND LITTLE SNAKE RIVERS. 



BY S. F. EMMONS. 



The region of the southwest corner of this map, which is drained by 

 the Yampa River and its numerous tributary streams, is in general a rolHng 

 country, of soft, rounded outhnes, well covered with soil and grass, and, along 

 the ridges, with a considerable growth of aspen, and a few pines. Along the 

 waters of most of the streams are wide alluvial bottoms, wliich, on the 

 Yampa River itself, afford considerable stretches of arable land, sometimes 

 nearly a mile in width, and which support a growth of fine, large cotton- 

 wood trees. This region is occupied by the soft and easily-decomposed 

 beds of the Cretaceous sandstones and clays, which, from the nature of 

 their composition, as Avell as that of the country itself, present compara- 

 tively few outcrops. The general outlines of their structure can, however, 

 be traced" by the forms of the ridges, which follow closely the lines of geo- 

 logical uplift. 



Near the flanks of the Park Range, however, where lower beds of the 

 Cretaceous come to the surface, the outcrops are largely concealed by over- 

 flows of volcanic rock, and larger accumulations of detrital material, due to 

 their proximity to high mountain-masses, and afford only vague suggestions 

 as to the structure of the sedimentary formations. At the head of Elk River 

 are broad openings in the forest, affording quite an expanse of meadow-land, 

 which is occupied by a considerable thickness of detrital gravel, composed 

 largely of ddbris of the soft sedimentary rocks, whicli have been exposed by 

 the eroding-off of the volcanic flows, and toward the mountains by debris 

 of the Archaean rocks. The fine gravels proceeding from the ^Archaean 

 range, at the head of the eastern fork of Elk River, have been washed with 

 considerable success for gold. 



In the deep ravine at the head of the west fork of Elk River are found 

 several outcrops of sedimentary rocks. At its mouth, where the stream 



