104: Waring — Lavas of Morro Hill and Yicinity. 



In the San Joaquin Hills, 7 or 8 miles south of Santa Ana, 

 and also in the Modena Hills, 5 miles northeast of Santa Ana, 

 small areas of lava have been examined bj E. S. Larsen, Jr., 

 in connection with geolog^ic mapping of the Corona Quad- 

 rangle for the U. S. Greological Survey, and found to be of 

 basalt, probably Miocene in age. Farther east, in the Santa 

 Ana Mountains, there are areas of greenstones, which Larsen 

 finds to be chiefly andesites and quartz latites, with minor 

 areas of basalts and rhyolites. They are intruded b}^ granite, 

 and are probably of early Cretaceous or pre-Cretaceous age. 



South of Morro Hill, in a zone extending approximately par- 

 allel with the coast, and widening to the south, there are areas 

 of felsitic intrusives, described by Fairbanks (pp. 7T, 86 and 

 92) and recently mapped in some detail by A. J. Ellis during 

 studies of the region for the U. S. Geological Survey. These 

 rocks are chiefly latites, and are tentatively classed by Ellis as of 

 pre-Cretaceous age. The only lava of later age in southwestern 

 San Diego County that was noted by Fairbanks or by Ellis is 

 on the shore, 3 miles north of La Jolla. A basaltic dike, there 

 exposed for a distance of 1800 feet, cuts Tertiary shales. It 

 varies in width from 2 feet at its northeastern exposed portion 

 to 30 feet in the southwest, where it disappears beneath the 

 surf. 



Gerald A. Waring, U. S. Geological Survey, 



Washington, D. C. 

 Clarence A, Waring, State Mining Bnrean, 



San Francisco, Cal. 



