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143-14 Stratigraphic Study of the Cajon Valley Formation in Southern California

Session: Sedimentary Geology Division/SEPM Student Research Poster Competition: Dynamics of Stratigraphy and Sedimentation

Poster Booth No.: 345

Presenting Author:

Johanna Quidangen

Authors:

Quidangen, Johanna¹, Strubel Iram, Ariel², Rodman, Joseph³, Chadwick, Alexandra⁴, Henriquez, Susana⁵, Sturmer, Daniel M.⁶, Ward, Dylan⁷, Dietsch, Craig⁸, Bidgoli, Tandis S.⁹, Todd, Claire E.¹⁰r> (1) Geological Sciences, California State University, San Bernardino, San Bernardino, CA, USA, (2) Environmental Science, Pitzer College, Pomona, CA, USA, (3) Geological Sciences, California State University, San Bernardino, San Bernardino, CA, USA, (4) Science and Math, San Bernardino Valley College, San Bernardino, CA, USA, (5) Geological Sciences, California State University, San Bernardino, San Bernardino, CA, USA, (6) Geosciences, University of Cincinnati, Cincinnati, OH, USA, (7) Geosciences, University of Cincinnati, Cincinnati, OH, USA, (8) Geosciences, University of Cincinnati, Cincinnati, OH, USA, (9) Geological Sciences, California State University, San Bernardino, San Bernardino, CA, USA, (10) California State University, San Bernardino, CA, ,

Abstract:

The Miocene Cajon Valley Formation (CVF), exposed north of the Cajon Pass alongside a railroad near the San Andreas Fault (SAF). The formation contains ~2,500 meters of middle Miocene clastic strata that filled a basin along the evolving paleo-SAF. Previous work on the CVF has focused on broad stratigraphic analysis dividing the formation into six members. Due to dominantly sandstone and conglomerate facies, the CVF has been interpreted as a braided fluvial environment. However, detailed facies analysis of CVF strata is lacking. In this study we begin to address that gap by completing and interpreting a series of measured sections within three members of the CVF. Reconstructing detailed sedimentary records in tectonically active regions provides foundational information for understanding changes in sedimentary conditions, including subsidence rates and sources over time.

In January 2026, we measured three stratigraphic sections through portions of the CVF, totaling to ~490 meters of section, including 194 meters from member 2, 126 meters from member 3, and 170 meters from member 5. Our data document overall fining-upward clastic stratigraphy composed primarily of cross-bedded and horizontally bedded medium to very-coarse sandstones locally interbedded with cross-bedded to lenticular bodies of granule-pebble conglomerates. Preliminary interpretations of the sedimentary environment suggest that all members record channel deposits in a braided fluvial system. Member 2 records sandy channels and a major gravel-dominated channel-fill sequence, member 3 records local overbank deposits in between minor sand-dominated channels, and member 5 records minor sand-dominated channels and sand flat deposits. Future work will focus on investigating the influence of autogenic and allogenic processes in the CVF and comparing depositional environment interpretations in the CVF with other strata of similar age exposed in other basins along the SAF.

Stratigraphic Study of the Cajon Valley Formation in Southern California

Description

Session Format: Poster

Presentation Date: 10/12/2026

Presentation Room: CCC, Hall F

Poster Booth No.: 345

Author Availability: 9:00 to 11:00 a.m.

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