RESUME. 
123 
The formations involved in the geology of the district include the 
Franciscan (Jurassic?) sandstone, shale, glaucophane schist, jasper, 
and intruded serpentine; Knoxville (lower Cretaceous) conglomerate, 
sandstone, and shale; pre-Monterey (which may include both Cre¬ 
taceous and older Tertiary) conglomerate, sandstone, and shale; 
Tejon (Eocene) sandstone, shale, and conglomerate; Vaqueros (lower 
Miocene) conglomerate, sandstone, and shale; Monterey (middle 
Miocene) diatomaceous and flinty shale, limestone, calcerous shale, 
and volcanic ash; Fernando (Miocene-Pliocene-Pleistocene) con¬ 
glomerate, sandstone, and shale; and Quaternary gravel, sand, clay, 
and alluvium. The sedimentary formations of Tertiary and early 
Quaternary age have a combined maximum thickness of at least 
13,200 feet. 
A variety of igneous rocks of Cretaceous and Tertiary age, mostly 
intrusive, outcrop over small areas. 
The Monterey shale (middle Miocene) is the original and chief 
oil-bearing formation, the petroleum having originated and remained 
in it in large quantities. Some has escaped by seepage and collected 
in the overlying Fernando formation or the Quaternary terrace de¬ 
posits, or has been dissipated. The oil is supposed to accumulate in 
fractured zones and porous sands in the lower portion of the Monterey, 
where brittle shale predominates, anticlines furnishing the most favor¬ 
able conditions for accumulation. The Monterey shale is in large 
part of organic origin, being especially rich in diatoms, and the oil 
is supposed to be a product of the plant and animal remains inclosed 
in it. The quantity of these remains originally deposited with this 
formation is sufficient to account for a vast amount of derived oil. 
Two structural systems prevail in the district, the features in the 
northeastern portion striking northwest and southeast, those in the 
southern portion striking east and west, and those in the intervening 
region trending in a direction intermediate between the two. Few 
faults of importance were noted in the field. The productive terri¬ 
tory lies in a region of more or less gentle folds in the central part of 
the area, most of the wells being located along or near anticlines. 
The wells range in depth from 1,500 to more than 4,000 feet. In 
the Santa Maria and Lompoc fields they obtain oil from zones of 
fractured shale, and possibly in certain places from sandy layers in 
the lower portion of the Monterey formation. The production of the 
individual wells ranges from 5 to 3,000 barrels per day, the average 
being between 300 and 400 barrels. The oil ranges in gravity from 
19° to 35° Baume, the greater part of it being about 25° to 27°. In 
the Arroyo Grande field the oil comes from sandstone at the base 
of the Fernando and is of 14° gravity. There is in all these fields 
much undeveloped territory which offers great promise of being 
