V.n.. VII] GF.STER— GEOLOGY McKJTTRICK DISTRICT 215 



sentecl by an overlapping- of the Tulare upon the underlying 

 Etchegoin sands. 



The lower dipping Tulare in the South-End McKittrick 

 field is seen within short distances to rest successively upon 

 Etchegoin sands and Santa Margarita shales. In some locali- 

 ties it cuts very abruptly across the edges of the former. In 

 fact it is only occasionally that any Etchegoin is to be found 

 exposed, for the Tulare usually extends far across the edges 

 of the older shale series. 



The fauna] break is even more apparent as is well exhibited 

 near the north line of the N. W. ^ Sec. 35. Here the Ano- 

 donta and Carinifex bearing sands are found dipping at 60° 

 within 200 to 300 feet of nearly perpendicular beds contain- 

 ing such forms as Pcctcn eldridgci, Pscudocarduiin gahhi, 

 Echinarachuius gibbsi, Nassa calif arnica, etc. 



RELATIONS TO PETROLEUM 



Throughout the whole extent of the West Side oil fields 

 some oil sands are found associated with the Tulare. The oil 

 sands are near the base and do not extend far up into the 

 series. It is an oil that has migrated into the Tulare sands 

 from the underlying beds and these sands are rarely pro- 

 ductive of oil in economic quantities in the fields south of the 

 Belridge. In several wells in the Maricopa flats fresh water 

 fossils have been found associated with tar sands above the 

 productive oil measures which in numerous localities contain 

 marine Etchegoin forms. 



In the Belridge field some of the oil and gas at least seems to 

 be derived directly from the sands within or at the base of the 

 Tulare. Many of the wells in the central part of the field on 

 Sees. 33 and 34 of Township 28-21 have thrown out large 

 quantities of sand saturated with oil and containing shells and 

 fragments of fresh water species such as 



Anodonta species. 

 Sphaerium. 

 Amnicola, etc. 



Among the wells producing oil from these fresh water 

 sands are wells Nos. 3 and 4 of the General Petroleum Co., 

 Sec. 3, Township 29-21 and several neighboring wells of the 

 Belridge Oil Co. 



