Masters Thesis

Structural geology of the Eastern Carrizo Badlands, north of the Coyote Mountains, Southern California

The Coyote Mountains in southern California lie within an ~70-km-wide dynamic boundary between the North American and Pacific tectonic plates known as the southern San Andreas fault system. The structure and stratigraphy of the range is the result of two distinct regional episodes of deformation (Dorsey & others, 2012): (1) late Miocene to Pleistocene transtensional faulting accommodated by the West Salton detachment fault in combination with the San Andreas fault to the east, and (2) Pleistocene to Holocene dextral strike-slip transpressional deformation related to the San Andreas, Elsinore and San Jacinto faults and fault zones. The stratigraphic sequence in the study area depicts a near-continuous depositional history of non-marine and marine sediments into the western Salton Trough between ~8.0 Ma and ~2.8 Ma due to the late Miocene to Pleistocene transtensional faulting. Additionally, evidence of extension-related deformation in the study area may be limited to two faults that show significant normal separation. Brittle and ductile deformation of sediments in the study area is consistent with prior interpretations of uplift and inversion of the Fish Creek–Vallecito basin as a result of initiation of the Elsinore and other strike-slip faults in the western Salton Trough ~1.2 Ma (Dorsey et al, 2011). The Andradé ladder structure is a previously unmapped and unknown ~7-km-wide ladder-like fault structure similar to the Durmid ladder structure within the San Andreas fault zone documented by Janecke and others (2018). The Andradé ladder structure is consistent with a zone of distributed right-lateral shear and rotation that accommodates the right-lateral deformation between the Elsinore and Painted Gorge faults.

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