PLEISTOCENE HISTORY OF SAN JUAN MOUNTAINS 387 
gravel deposits suggestive of glaciation in more remote Pleistocene 
times. Satisfactory evidence of an earlier epoch of glaciation was 
found in the progress of the field work for the Ouray folio.t It is 
noteworthy that these deposits on the north side of the range which 
were undoubtedly formed during an epoch of glaciation preceding 
the last occupation of this range by ice are apparently of greater age 
than those made by the “earlier ice” of the mountain groups cited 
above. ‘They are in harmony with the scattered deposits found in 
the Bighorn and Sawatch ranges which suggested a third and still 
earlier glaciation, rather than with the earlier of the two well- 
defined epochs which have been noted in several of the Cordilleran 
mountain groups. A fuller statement regarding these deposits will 
be given later in this paper. More recently, in the Engineer 
Mountain quadrangle of the San Juan Mountains, evidence of two 
glacial epochs has been recognized.” 
Work upon which the present paper is based.—In 1910 the glacial 
deposits of the La Plata, Animas, Florida, Vallecito, and Pine 
valleys on the southern and southwestern slopes of the San Juan 
range were studied in detail and these studies revealed the evidence 
of two distinct glacial epochs.’ 
In rorr similar studies in the valleys of Weminuche and Huerto 
creeks and the Piedra River, on the southeastern, of the Rio Grande 
on the eastern, and of the Uncompahgre and Dallas, on the northern 
slopes of the range, have resulted in the finding of evidence which will 
be presented as proof of three distinct glacial epochs in the history 
of this mountain group. 
Nomenclature.—It is not as yet possible definitely to correlate 
the glacial epochs among the mountains with those of the conti- 
nental ice sheets, and even if such a correlation could be correctly 
made it may prove desirable to have different names for the epochs 
associated with the two types of glaciation which existed on this 
continent during the Pleistocene period. Throughout this paper 
the three epochs now known to have existed in the San Juan area 
will be referred to by the names which were applied and used in the 
t Howe and Cross, Bull. Geol. Soc. Am., XVII (1905), 251-74; Cross and Howe, 
U.S. Geol. Survey, Folio 153 (1907). 
2A. D. Hole, U.S. Geol. Survey, Folio 171 (1910). 
3 W. W. Atwood, Jour. Geol., XTX (1911), 449-53. 
