34 CALIFORNIA ACADEMY OF SCIENCES [Proc. 47H Ser. 
As to the exact period to which these results of base-leveling 
are to be attributed it is not easy to say with certainty. While 
presumably the greater part of it was accomplished during the 
Pleistocene, part has undoubtedly been the result of Pliocene 
denudation, and part has occurred later. 
Whitney’ has classed the buried river channels of the Sierra 
Nevada as belonging to the later Pliocene period, and in this 
view both Lindgren* and Lawson* have acquiesced. With 
these river channels may be correlated the Tulare deposits 
of the Great valley, while the development of the great 
Sierran peneplain most writers consider to have taken 
place later. 
The Pleistocene Deposits——The deposits of the Pleistocene 
consist for the most part of alluvial fills or other superficial 
deposits of boulders, gravels, and sands. These deposits are 
especially abundant at the southern end of the Great valley, 
where they have been noted by Whitney, who mentions also 
the terraces about the Tejon ranch, though he does not desig- 
nate them as such. The gravel and boulder deposits of the 
San Emidio canyon he also describes in part, and illustrates 
them by a sectional profile clearly showing their unconform- 
able relation to the Tertiary formations and to the base-leveling 
of the adjacent foothills. In the neighborhood of the Midway 
oil district is a comparatively wide plain to the west of Buena 
Vista lake at an elevation of 600 feet above the valley, which 
is largely the product of alluvial filling and base-leveling of 
the surrounding Tertiary hills. The same class of facts is 
observable at McKittrick, Temblor, Carisa valley, Cholame, 
Peachtree, and elsewhere. 
These deposits are never clearly stratified and are of the 
nature of alluvial accumulations on land surfaces, rather than 
in submerged basins. As in the case of the terraces, they have 
been considerably obscured by the products of later denuda- 
tion, and it is not always easy to distinguish the Pleistocene 
from recent deposits. In many places, as at San Emidio, 
1 Geol. Sury. Calif. Geol. v. 1, p. 250 et seq. 
2 Journ. Geol. v. 4, p. 905. 
3 Bull. Dept. Geol. Univ. Calif. v. 1, p. 157. 
4 Geol. Surv. Calif. Geol. v. 1, pp. 188, 191 ef seq. 
