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Geologic and Geomorphic Evidence for Possible Reactivation Along the Dry Creek Fault Zone and Hoadley Fault, Cryptic Faults in the Northern Sacramento Valley and Surrounding Areas

Description: 

Observations along the Dry Creek fault zone (DCFZ) and Hoadley fault (HF) suggest that there are cryptic, Quaternary faults present throughout the northern Sacramento Valley and into the southern Klamath Mountains. Bedrock mapping along the DCFZ identifies distributed folds, fractures, and faults in pre-Tertiary bedrock across a deformation zone approximately 3 km wide and 12 km long located north of Redding, CA. Extended, interconnected surface lineaments may be 38 km total length. Surficial geomorphic mapping does not identify discrete surface displacements in late Quaternary erosional surfaces and fluvial terraces along the DCFZ. Instead, a broad deformation zone in bedrock is oriented sub-parallel to Inks Creek fold belt structures. A fault strand on the northwestern margin of the zone generally coincides with the alignment of several Quaternary surface back edges that form a diffuse, irregular escarpment. On the south side of the deformation zone, a heavily weathered, unlithified sedimentary deposit identified on an intermediate terrace in the Sacramento River sequence appears to be in fault contact with Paleozoic bedrock. The deposit appears to predate the terrace and its age is uncertain. Absent some topographic expression, deformation in other Tertiary to Quaternary deposits or surfaces indicates deformation probably predates the terrace sequence, which is younger than ~0.8 Ma.

Southwest of Whiskeytown Reservoir, a subtle northwest-striking, irregular, and discontinuous escarpment crosses Quaternary fan surfaces in the Boulder Creek drainage along the northern strand of the Hoadley fault in the southern Klamath Mountains. The escarpment is subparallel to ridgelines, bedrock foliations, and is mapped as a normal fault. There is up to ~10 m of vertical separation along the escarpment and is consistent with a normal sense of motion. Nearby exposures did not have clear evidence of faulting in boulder-rich fan deposits. Together, these observations point to late Cenozoic re-activation of multiple faults at different orientations in the relatively low-strain setting of north-central California.

Session: Cryptic Faults: Advances in Characterizing Low Strain Rate and Environmentally Obscured Faults [Poster Session]

Type: Poster

Date: 5/1/2024

Presentation Time: 08:00 AM (local time)

Presenting Author: Wesley

Student Presenter: No

Invited Presentation: 

Authors