GRAVITATIONAL METHODS 



433 



either flank. Such light material is probably sufficient to account for the 

 Lost Hills gravity minimum. 



The same Reef Ridge formation farther to the north as found over the 

 Kettleman Hills area is appreciably thinner, as only from 600 to 800 feet 



Fig. 262. — Residual gravity, Lost Hills-Kettleman Hills Area, California. Contour interval 

 0.5 mg. (Geophysics, Vol. XI, No. 2, April, 1946, p. 124.) 



of it are present. Moreover it is here composed of harder shales, clays and 

 sands than at the Lost Hills locality. 



The formation below the Reef Ridge is the McClure Shale. It is rela- 

 tively hard and dense, both at the Lost Hills and at the Kettleman Hills. 

 It would appear to influence the gravity picture only to the extent that it 



