We've Moved!
Visit SDSU’s new digital collections website at https://digitalcollections.sdsu.edu
Description
The structural geometry and kinematics of structures associated with a prominent splay off the newly discovered and mapped Taylor Lake fault zone, Picacho State Recreation Area, SE California, may provide evidence for changing plate boundary conditions during Miocene time. Two prominent hypotheses exist as to how Baja California separated from mainland Mexico. According to Stock and Hodges (1989) Baja moved obliquely away from mainland Mexico as a result of partitioning ~350 km of strike-slip motion along the San Benito-Tosco-Abreojos fault zone and ~160 ± 80 km and 110 ± 80 km of ENE extension within the Gulf Extensional Province. Gans (1997) however noted that large scale extension in the Gulf Extensional Province predates the ~ 15 - 6 Ma time frame in which Baja was transferred to the Pacific plate. Detailed mapping of a small part of the Taylor Lake fault zone resulted in the recognition of the Little Picacho Wash splay. This splay subdivides the study area into western and eastern blocks. Cross-sections and plots of poles to beds indicate that the western block hosts an approximately cylindrical open upright SW plunging anticlinesyncline pair that is truncated by the Little Picacho Wash splay. These characteristics however are not preserved across the splay into the eastern block where cross-sections reveal a complex geometry caused by high strain resulting from the eastern block being forced SE into the wedge defined by the Taylor Lake fault and the Little Picacho Wash splay. These and other data discussed herein favor the model of Gans (1997) in which intracontinental Middle to Late Miocene distributed dextral shearing allows Baja to separate from mainland Mexico.
