GSA Connects 2021 in Portland, Oregon

Paper No. 194-13
Presentation Time: 2:30 PM-6:30 PM


MORGAN, George, 4671 Lee Ave, La Mesa, CA 91942 and PRALL, John

An east-west trending group of exposures, interpreted as a flat bottom, Miocene aged paleo-channel (PC), formed by a west flowing drainage, has been mapped in the Coyote Mountains. The sides of the PC are confined, for the most part, by basement units. This PC has been linked to the second episode of extension associated with the southern Basin and Range Province. The Miocene aged normal (listric) Nickel Prospect Fault cuts the PC, into western (graben) and eastern (horst) groups of exposures. Under the eastern and western portions of the PC are, locally derived, Miocene aged marine and subaerial units of the Viejo Formation (Mv). Deposited in the PC, on both sides of the Fault, is a thick (200+ feet), locally derived, subaerial Garnet Fanglomerate Member of the Mv. This subaerial unit has been mapped as Quaternary in age by Christensen (1957), Ewing (2014), Smart (2018) and Bykerk-Kauffman et al. (2018). Winker and Kidwell (1996) mapped the subaerial gravels as Miocene. On both sides of the Fault, conformably deposited on the Garnet Fanglomerate is the near-shore marine, Miocene aged, Garnet Member of the Mv. Unconformably deposited on the Garnet Member, on both sides of the Fault, is the near-shore marine, Miocene aged, Upper Garnet Member of the Mv. The Garnet Fanglomerate, Garnet and Upper Garnet Members appear to be unique to the PC. The PC is erosionally truncated in the central part of the horst. 1.2 km to the east of the truncation, in different graben produced by the Miocene aged, normal (listric) Amphitheater Fault, is a similar, Miocene aged PC. We believe this second PC is a continuation of the truncated PC to the west.

Bykerk-Kauffman, A., Lucas, S. and Smart, J., 2018, The Painted Gorge fault, a potentially active dextral fault in the northeastern Coyote Mountains, Salton Trough, Calif.: GSA Abstracts with Programs. Vol. 50, No. 5.

Christensen, A. D., 1957, Part of the geology of the Coyote Mountains area, Imperial County, Calif.: Unpublished M.S. Thesis, University of California at Los Angeles, 188p.