76 
SANTA MARIA OIL DISTRICT, CALIFORNIA. 
For convenience the two quadrangles will be divided into the three 
naturally separated portions outlined in a preceding paragraph, viz, 
the region of the San Rafael Range, which includes all of the territory 
northeast of the Santa Maria Valley and a line extending southeast 
of its head; the region of the Santa Ynez Range; and the province 
of low hills and shallow valleys intervening between the two moun¬ 
tain masses. The reading of the following paragraphs describing the 
structure of various areas should be accompanied by reference to the 
map. (PL I, in pocket.) For the sake of compactness the conclu¬ 
sions as to the possibilities of productiveness of the Monterey shale 
have been stated, together with the description of its main structural 
features. 
It must be remembered that in regions of great disturbance such as 
the shales have undergone in some parts of the area it is difficult to 
represent by single lines the complexity of the structure. Some of 
the lines, therefore, mark zones of folding rather than single definitely 
continuous folds. The dotted lines of structure are purely supposi¬ 
tional. 
REGION OF THE SAN RAFAEL MOUNTAINS. 
AREAS OF ROCKS OLDER THAN THE MONTEREY. 
Whatever succession of beds or structural conditions may once 
have existed in the Franciscan formation (Jurassic?) in this district, 
they have been largely obliterated by the successive folding and 
crushing to which these rocks have been subjected in the long period 
of time since their first uplift. The shales and sandstones mapped as 
pre-Monterey, especially where the beds alternate, have preserved the 
folds well, but except on North Fork of Labrea Creek and along Sis- 
quoc River no effort has been made to work out the structure of this 
series. 
AREAS OF MONTEREY AND LATER FORMATIONS. 
FOLDS. 
Considered as a whole the Monterey has been thrown into a series 
of anticlinal and synclinal folds striking about N. 50° W., and appar¬ 
ently plunging, in the main, toward the northwest. Great variation 
exists in the relative steepness of dip along these folds, but it is evident 
that the compressive forces producing them were of much greater 
strength in the southeastern part of the area, between Bone Mountain 
and Round Corral Canyon and thence southeastward into the region 
of Zaca Peak. Here the folds become so compressed and in places 
overturned that it is difficult to trace them. PI. Ill, B (p. 34) and 
VI, B (p. 46) give an idea of the closeness of the folding. In contrast 
with this constricted portion is the broad series of folds which extend 
