STRATIGRAPHY OF SOUTHERN CALIFORNIA 129 
Harford, San Luis Obispo county, where the deposits of shells 
in the adobe soil attain a thickness of over six feet. 
SAN DIEGO. 
General geology — Next to San Pedro, the best development 
of the marine Pleistocene of Southern California is found in the 
vicinity of San Diego. The geologic history of San Diego has 
been somewhat similar to that of the San Pedro region. During 
late Pliocene times the territory now occupied by San Diego 
Bay and the region to the northwest was occupied by an arm of 
the sea in which were deposited several hundred feet of coarse 
gravels, and these in turn were overlaid by fine grained sand- 
stones. An uplift took place at the close of the Pliocene or in 
early Pleistocene times, followed by a period of erosion during 
which the terrace or mesa which extends from San Diego to 
Pacific Beach was planed off. Following the period of uplift a 
slight depression took place, and the gravels and sands of the 
upper San Pedro series (Pleistocene) were laid down on top of 
the eroded Pliocene sandstone. Since the deposition of the 
latest beds an uplift of at least fifty feet has taken place. 
Pliocene.— The writers have examined the Pliocene strata at 
Pacific Beach, and near the Russ School (San Diego well). The 
Pliocene at Pacific Beach makes the lower part of the sea cliff 
which begins at Ocean Front and extends northward for at least 
a mile and ahalf (see Fig. 4). Two hundred feet of yellowish- 
brown sandstone, dipping south at an angle of about Io degrees 
and overlain unconformably by Pleistocene gravel, are exposed 
in this section. The upper layers of the sandstone are fossilifer- 
ous, while the lower portion, which rests on an unknown thick- 
ness of coarse gravels, is without fossils. 
There are two horizons in the fossiliferous section of the 
sandstone which may be separated upon paleontologic evidence. 
The lower horizon comprises all of the exposed fossiliferous 
beds with the exception of the uppermost three or four. It is 
characterized by a unique fauna among which are found the 
following species which are not known outside of the San Diego 
