28 Geologic Mapping in the West (Posters)

This poster session highlights geologic mapping in the western Cordillera and Rocky Mountains. We encourage submissions that explore bedrock and surficial geology, geophysics, hydrology, hazards, and more. Both professional and student submissions are welcome.

Tuesday, 19 May 2026
8:00 AM - 5:30 PM
Alvarado D/E

Quaternary Evolution and Bedrock Structure of the Southern Great Salt Lake Shorezone in the Mills Junction Quadrangle, Utah

Paper number: 28-7
Program: Technical Sessions
Time: 8:15 AM – 8:15 AM

Authors

Abstract

The Mills Junction 7.5' quadrangle is in Tooele Valley on the southern margin of Great Salt Lake (GSL), 20 miles west of Salt Lake City, Utah. The area’s population is expected to grow to 150,000 by 2060. The quadrangle contains the transition of the Holocene-active Oquirrh-Great Salt Lake fault zone from the depths of GSL to a range-bounding fault cutting Pleistocene Lake Bonneville deposits on the western margin of the Oquirrh Mountains. Recent lidar-based fault mapping identified additional Holocene-active faults on the valley floor cutting younger alluvium within undeveloped areas of the quadrangle. Most surficial deposits are lacustrine and range from Lake Bonneville sediments to Holocene and modern GSL shorezone deposits, including ooids, spring-fed carbonates, and microbialite reefs. Lake Bonneville shorelines etch the Erda salient, which is cored by shallow Paleozoic Oquirrh Group limestone and sandstone. The bedrock shows variable deformation, from brecciated on the Erda salient to folded and overturned at the northern tip of the Oquirrh mountains. We interpret a previously unmapped conglomerate South of Adobe Rock, a historical marker on the Erda salient, as Tertiary basin fill, containing mostly angular Oquirrh Group clasts cemented by carbonate. An 84-ft sediment core (BE-1) was recovered while drilling a groundwater monitoring well along the playa of GSL. The core was split, photographed, and scanned for magnetic susceptibility and x-ray fluorescence. Subset samples (n = 65) were extracted for magnetic susceptibility refinement measurements and/or micropaleontology to identify and interpret pre- and post-Bonneville depositional conditions. BE-1 contains a succession of poorly sorted angular sands, bioturbated marls, finely laminated mud couplets of aragonite and clay, a basaltic ash layer, and intrasediment gypsum beds near the top. This poster highlights the geologic mapping and subsurface and preliminary core interpretations.

Geological Society of America Abstracts with Programs. Vol. 58, No. 4

doi: 10.1130/abs/2026RM-410611

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