30 
SANTA MARIA OIL DISTRICT, CALIFORNIA. 
its rocks stratigraphically below the base of the Monterey (middle 
Miocene) shale. 
Strata corresponding to the upper portion of the Tejon-Sespe- 
Yaqueros terrane have been recognized also in the San Rafael Moun¬ 
tains, where they are exposed at the base of the Monterey (middle 
Miocene), and it may be that the pre-Monterey rocks are in part 
equivalent to the lower portion of this terrane. The Yaqueros and 
possibly part of the Tejon are present also in the Casmalia Hills. 
LITHOLOGIC CHARACTER. 
The lower portion of the terrane is made up of a thick series of 
greenish-gray coarse and fine sandstones, many of them concretion¬ 
ary in character, interbedded with dark, fine-grained, thin-bedded 
shales in lesser amount. Toward the middle of the terrane the shale 
increases in amount, alternating with thin beds of sandstone. Much 
of the shale has a characteristic olive-gray color, and owing to its 
hard, gritty, brittle nature it makes excellent road material for the 
Santa Ynez Yalley. The shales and sandstones give place above 
the middle of the terrane to deposits of shallow-water character— 
coarse sandstone and a great quantity of coarse, in many places green¬ 
ish or reddish, gravelly conglomerate. This conglomerate contains 
abundant Yaqueros fossils and probably represents the base of that 
formation and a period of shallow-water conditions with which the 
Yaqueros began. The conglomerate gives place in turn to more 
•shale and sandstone, which continue to the summit of the terrane. 
At the top there is a conformable gradation into the Monterey (mid¬ 
dle Miocene) beds, the summit of the Yaqueros being marked by a 
calcareous zone in many places—as, for instance, southwest of Lom¬ 
poc, where the two formations are divided by a very prominent 
exposure of hard limestone. This limestone is quarried and used in 
the refining of beet sugar. Sandstone, shale, and conglomerate 
belonging to the Tejon-Sespe-Vaqueros terrane occur at the seaward 
end of the Casmalia Hills. They form a series conformably under¬ 
lying the Monterey (middle Miocene); but they are separated from 
beds of flint and shale that can be definitely assigned to the latter 
formation by an intervening horizon many hundred feet thick of 
soft, light-brown, clayey, alkaline shale that is almost invariably 
full of crystalline gypsum. Here the conditions existing during the 
period of transition from typical Yaqueros to typical Monterey sedi¬ 
mentation must have been very different from those prevalent over 
the areas occupied by the Santa Ynez and San Rafael ranges. Acidic 
volcanic ash is interbedded with the Tejon-Sespe-Yaqueros strata 
in the Casmalia Hills. The occurrence of the ash and the alkaline 
