The paper discusses the importance of the overlaps in the southern part of the San Joaquin valley. Two of these overlaps are of remarkable magnitude: one existing at the base of the Vaqueros (lower Miocene) and the other at the base of the Santa Margarita (uppermost Miocene).

Each overlap was preceded by an intense folding, and the structural features in these different periods of folding are evidently independent of each other.

This is well illustrated in the lower Santiago Canyon in the San Emigdio district where Vaqueros beds are folded into an anticline that is not reflected in an underlying, apparently monoclinal, series of Oligocene beds. Not far from this locality a broad syncline of Etchegoin (Pliocene) overlies vertical beds of Vaqueros.

The great overlap of the Santa Margarita and Etchegoin brings these formations into contact with all the older ones. They are therefore able to accumulate the oil produced in different strata of the older rocks. This may explain the great quantities of oil now present in the Etchegoin, without making it necessary to admit that the oil accumulated by migration over long distance.