400 WALLACE W. ATWOOD AND KIRTLEY F. MATHER 
separated portions of the range (1) near the southeast margin in 
the valleys of the Piedra and certain of its tributaries, (2) at the 
eastern side of the range in the Rio Grande Valley, and (3) at the 
northwest in association with the valley of the Uncompahgre and 
the plateau of the same name. The first suggestion that there was 
evidence of a third and much earlier epoch of glaciation in this range 
than had been determined in the Cordilleran region of North 
America was secured from the paper by Howe and Cross, so often 
referred to above.t_ From an inspection of the maps it appeared 
that if the mantling material of Horsefly Peak was indeed glacial 
that it must belong to an epoch of glaciation far removed in time 
from the known glacial epochs of the western mountains. The 
first determination by the present authors of three distinct epochs 
was, however, made near the headwaters of the Piedra River. In 
that region, on the intervalley areas, high above the present streams 
and beyond the terminal moraines of the two later epochs, there are 
much older glacial deposits. The distribution of these deposits 
has been indicated on Fig. 2. 
The morainic deposits on the west side of Huerto Creek, a few 
miles above the Piedra, are, in part, fully 1,000 feet above the 
Huerto stream channel. They mantle the slope toward the stream 
in great landslide masses which appear to have come down in very 
recent times. In this deposit there are bowlders up to 9g feet in 
diameter and striated material is not uncommon. On the ridge 
between Huerto and Spring creeks the ancient glacial bowlders 
occur in abundance and in association with them there is a consider- 
able body of finer drift. Some of the stones in this drift are 
striated. The deposit on the west side of Huerto Creek appears to 
have come from the headwaters of the Piedra to the north eastward, 
and it is inferred from the relationship of these deposits, from the 
absence of the marks of glaciation in Huerto Creek canyon, and from 
the distribution of other deposits interpreted as of the same age, 
that the ice which left these deposits advanced over a surface which 
corresponded to the elevation of the intervalley ridges, and that 
the thousand-foot canyon of Huerto Creek has been excavated since 
the melting away of that ice. 
* Bull. Geol. Soc. Am., XVII (1905), 251-74. ‘ 
