SCEC Award Number 25225 View PDF
Proposal Category Individual Research Project (Single Investigator / Institution)
Proposal Title Measuring differential uplift rates across multiple fault strands in the San Gorgonio Pass region using thermoluminescence thermochronology
Investigator(s)
Name Organization
Nathan Brown University of Texas, Arlington
SCEC Milestones A1-3 SCEC Groups Geology, SDOT, PBS
Report Due Date 03/15/2026 Date Report Submitted 04/01/2026
Project Abstract
 I propose to measure in situ bedrock outcrop erosion rates on 12 samples from both sides of the Galena Peak, Mission Creek, and San Bernardino fault strands in the San Gorgonio Pass (SGP) region using low-temperature thermoluminescence (TL) thermochronology, a technique I helped develop during my PhD. I have previously measured this signal from 24 bedrock samples nearby, across the Mill Creek and Galena Peak fault strands on the northern side of the Yucaipa Ridge block to reveal a significant erosion rate contrast across the Galena Peak fault since at least 50 ka. Four of these samples were already collected in an earlier field season and 8 more would be collected for this project, by myself and my PhD student, Ayush Joshi. This technique is sensitive to a wide range of erosion rates on timescales of 10-100 ka, and prior work has shown that bedrock erosion rates in the southern San Bernardino Mountains are primarily controlled by tectonic uplift rates on timescales ranging from 100 to 103 ka. Therefore, if we observe any systematic differences in bedrock erosion rate across any of these fault strands, we can infer differences in tectonic uplift on timescales relevant for fault reorganization in this area. As the SGP currently has very few geologic constraints on tectonic activity on Late Pleistocene – Holocene timescales, and as this region is critical for interpreting regional fault dynamics and seismic scenarios, it would benefit the SCEC community to develop this novel dataset.
Intellectual Merit This project demonstrates for the first time that thermoluminescence (TL) thermochronology can resolve the landscape response to tectonic forcing on 10 – 100 ka timescales. In bedrock landscapes, this technique stands as one of the only methods to quantify the evolution of tectonic blocks. We observe elevated erosion rates near some fault traces and not others. Which fault strands are erosionally active evolves through time. We hypothesize that this is related to changing levels of seismic activity in the past.
Broader Impacts I enrolled my university (UTA) to be a SCEC Participating Institution. This project supported my Ph.D. student, Ayush Joshi, and I am an Early Career faulty at a Minority Serving Institution. This project advances our understanding of Late Pleistocene - Holocene seismic potential along multiple strands of the greater southern San Andreas fault system, in the San Gorgonio Pass region.
Project Participants Myself (Brown) and my Ph.D. student, Ayush Joshi.
Exemplary Figure Figure 1. Thermoluminescence (TL) sample locations collected previously (squares) and for this study (circles) are colored by their apparent erosion rates. These are shown for: (a) the most recent resolved time period of 10-20 ka, (b) the oldest resolved time period of 90-100 ka, and (c) the maximum erosion rate within the entire 10-100 ka interval. Sample names are shown in (a) and major structures are shown in (b).
Linked Publications

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