TERTIARY DEPOSITS NEAR COALINGA OIL FIELD 35 
MIOCENE 
The character and divisions of the Miocene in this region have 
been quite fully described in the publications referred to and espe- 
cially by Messrs. Arnold and Anderson in the Bulletins of the United 
States Geological Survey. The divisions present in this area are as 
follows: 
5. Etchegoin 
4. Jacalitos 
3. Santa Margarita 
2. Monterey ? 
I 
. Vaqueros 
I. VAQUEROS 
The Vaqueros comprises all beds found between the Tejon and 
the Big Blue, the basal non-fossiliferous member of Santa Margarita 
of Arnold. It is predominatingly sandy, with conglomerate at 
base, and very fossiliferous as a whole. It lies with marked uncon- 
formity upon the Tejon. The basal unconformity which has been 
described and fully illustrated elsewhere is marked in Twp. 17 S., 
R. 14 E., by the absence of its lower beds, the upper portion resting 
directly on the Tejon white shale. 
Ze MONTEREY 
The series of light-gray, fine-grained sand and clay that appear. 
bluish when moistened, which lies between the Vaqueros and Santa 
Margarita, has been called the “‘ Big Blue” and its possible Monterey 
age has been suggested by Arnold, who classed it tentatively with 
the Santa Margarita. It has a thickness of nearly 300 feet in the 
oil field, but appears to be somewhat thinner toward the northwest. 
It is clearly separated from the Vaqueros beds below and the Santa 
Margarita above. 
In Twp. 17 S., R. 14 E., it occurs as bluish shales that in places 
are variegated reddish and yellow, succeeded by sandy bluish shales 
intermixed with gravel, having a total thickness of about 200 feet. 
The shales are unfossiliferous here as elsewhere, but are easily 
separable from the Santa Margarita, since the basal conglomerate 
of that formation contains a wealth of typical Santa Margarita 
fossils. 
The stratigraphic position of the Big Blue north of Coalinga is 
