New Geologic Maps of the Puente Hills, Southern California
T. W. Dibblee1 and H. E. Ehrenspeck2
1Dept. of Geological Sciences, Univ of California at Santa Barbara, Santa Barbara, CA
2Dibblee Geological Foundation, Goleta, CA
Four new contiguous 1:24000-scale geologic quadrangles by Thomas W. Dibblee, Jr. ae now published as 2 maps of the Puente Hills of southern California. These quadrangles, from west to east, are Whittier, La Habra, Yorba Linda, and Prado Dam, of eastern Los Angeles County and parts of Orange, San Bernadino and Riverside counties. Dibblee mapped this region for Richfield Oil Company in 1943–44, prior to the widespread petroleum resource development and urbanization of this area. He also mapped with a purpose and perspective different from that of the US Geological Survey was to follow. Thus, Dibblee’s observations and interpretations pertaining to structure and stratigraphy differ, in places significantly, from the published USGS mapping of the 1960s of the same area and there exist intrinsic values in showing the differences.
The western 3 quadrangles of the east-west-trending Puente Hills uplift expose only middle to late Cenozoic, mostly marine sedimentary rocks. The oldest rocks are of the middle Miocene Monterey Formation (a.k.a. Puente Formation) conformably overlain by the late Miocene to Pliocene Sycamore Canyon and Fernando Formations, then the early Pleistocene shallow marine San Pedro Formation. These strata are unconformably overlain by nonmarine alluvial sediments of the La Habra Formation, which is overlain by old and young surficial units.
All these bedrock and surficial units are exposed along the active major Whittier fault of right lateral, north-side-up displacement that transects the region from northwest to southeast. Many minor drag folds, generally trending northeastward and dying out rapidly away from the Whittier fault, have complexly folded the section north of it. In the eastern Puente Hills of the Prado Dam quadrangle and southward, successively older formations, the middle Miocene Topanga, early Miocene Vaqueros, Oligocene Sespe, and several Eocene to Cretaceous-Jurassic sedimentary and volcanic units are exposed immediately south of the Whittier fault. The Puente Hills uplift is terminated quite abruptly to the east, in the Chino Hills by the northwest-trending right-lateral Chino fault.
AAPG Search and Discovery Article #90904©2001 AAPG Pacific Section Meeting, Universal City, California