SANTA CLARA VALLEY: SESPE FIELDS. 
53 
this locality. The lower Fernando is not exposed, but its outcrops 
cover considerable areas to the west and isolated areas also appear 
to the east, notably at the point of the foothills immediately east of 
Fillmore and in the vicinity of Pirn. East of Piru the Fernando 
becomes the prevailing formation. 
A stratigraphic feature that has considerable significance in con¬ 
nection with the geologic history of the Sespe region is the disappear¬ 
ance of the lower Modelo sandstone. In the area about the head of 
Hopper Canyon this terrane has an enormous development, its thick¬ 
ness amounting to at least 4,000 or 5,000 feet. Within the Sespe oil 
fields, however, its maximum is barely more than 1,000 feet and it 
disappears entirely in the slopes of Sespe Valley south of Oat Moun¬ 
tain. * At other points within the confines of the oil fields it passes 
beneath the Surface while still strongly developed, and its ultimate 
behavior is of course unknown. 
The range south of Santa Clara River is seemingly a development 
independent of, though perhaps synchronous with, the mountains 
north of the river. There is, however, a degree of geologic relation¬ 
ship shown by the recurrence in the lower slopes of Oak Ridge of beds 
that from a paleontologic standpoint are undoubtedly the homologues 
of the lower portion of the lower Miocene which is encountered on 
Fourfork and Tar creeks. Below this paleontologic horizon in other 
portions of Oak Ridge, particularly to the west, still lower measures 
are exposed, consisting of brightly banded red and gray sandstone 
and sandy clay and heavier cross-bedded and somewhat conglomeratic 
rusty sandstone. This series is in general appearance very different 
from the Sespe beds north of the Santa Clara, yet in some of the details 
there is considerable resemblance. It would seem, therefore, that 
the horizons mentioned are repeated in the two localities, but with a 
certain differentiation of sediment and a reduced thickness to the south. 
Suggestions of such reduction are found even north of the Santa 
Clara in the westerly slope of Oat Mountain, where the Vaqueros 
and Modelo formations are perceptibly thinner than in their type 
localities. 
The foregoing description of structure about Sespe Canyon is the 
result of a reconnaissance made with reference to the mode of occur¬ 
rence of petroleum in the several localities in which it has been found. 
Detailed work, careful examination of individual strata for their fossil 
contents, and the tracing of the several horizons should lead to a much 
clearer understanding of the complexities that exist and might even 
alter the present exposition of some of the features. In the main, 
however, it is believed that the view presented is correct, and so far 
as it bears on the occurrence of petroleum it may be accepted. 
Bull. 309—07-5 
