Structural and Sedimentological Analysis of the Bear Canyon Conglomerate, Southeastern California: Implications for the Timing and Style of Miocene Deformation within the Eastern California Shear Zone
The region between Indian Pass and Picacho State Recreation Area (PSRA) in southeastern California records complex deformation related to the transition from a Paleogene convergent margin to a Neogene transform setting, although the timing and nature of youngest deformation in this region remains incompletely known. A 1.7 km-thick section of Miocene Bear Canyon conglomerate (BCC) was studied to constrain this young period of deformation. These rocks lie unconformably upon 23 Ma volcanic and epiclastic rocks and a Mesozoic metamorphic basement terrane. Near PSRA the BCC contains locally derived clasts and can be further subdivided into three unconformity-bounded sequences, referred to as sequences I, II, and III from oldest to youngest. At Indian Pass, the 9.45 ± 0.27 Ma basalts of Black Mountain are interstratified with the upper part of the BCC, though it was unknown how these relationships extend to PSRA where detailed mapping had established the stratigraphic architecture of this unit. The BCC itself has been internally faulted and folded and preserves a set of NW-striking dextral faults, a set of NE-striking sinistral faults, and the prominent EW-trending Copper Basin reverse fault. This project builds upon previous results by investigating BCC subdivision and provenance, continued mapping south of the Copper Basin fault and west of where the fault becomes elusive. These key details and their relation to the basalts of Black Mountain support and rectify gaps in existing studies. Initial results suggest that east-west extensional stresses ceased ~17 Ma and were replaced by north-south shortening ~10-12 Ma. Sequence I of the BCC was deposited between 23 and 9.45 Ma, prior to deposition of the basalts of Black Mountain. These basalts lie between sequence II and III of the BCC. Sequence III near PSRA preserves numerous faults and folds, which appear to record north-south contraction. These observations suggest that the BCC records onset of deformation related to development of the San Andreas transform margin.
Goff, Garrett, "Structural and Sedimentological Analysis of the Bear Canyon Conglomerate, Southeastern California: Implications for the Timing and Style of Miocene Deformation within the Eastern California Shear Zone" (2019). ETD Collection for University of Texas, El Paso. AAI27671777.