31 Best Student Geologic Map Competition (Posters)

Students will present their research through geologic mapping projects (with a significant field mapping component) that address scientific or societal issues. The top three student-authored geologic maps will receive awards following this session.

Sunday, 19 October 2025
8:00 AM - 5:30 PM
HBGCC, Hall 1

Insights on source, timing, and depositional conditions of the Spruce Mountain landslide from mapping in the Spruce Well 7.5’ Quadrangle, south-central Elko County, Nevada

Paper number: 31-12
Program: Technical Sessions
Time: 8:00 AM – 8:00 AM

Authors

Abstract

New geologic mapping of the Spruce Well 7.5’ quadrangle in Nevada reveals new insights into the composition, source, and timing of the informally named Spruce Mountain landslide. A combination of remote sensing, field mapping, and geochronologic methods, including tephrochronology, 40Ar/39Ar dating, and 36Cl and 10Be cosmogenic dating, constrain the age of the deposit and help differentiate units within and underlying the landslide deposit.  

The landslide deposit was sourced from the peak of Spruce Mountain, which is a 3.5 km-long ridge located 3.75 km east of the study area. The landslide had a drop of ~1.4 km with a maximum runout distance of ~11.5 km. The landslide deposit is predominantly limestone breccia of the Devonian Guilmette Formation, with notable input from the Ordovician Pogonip Group, Ordovician Eureka Quartzite, and Mississippian Diamond Peak and Pennsylvanian Ely formations.

Field mapping and differentiation using topographic roughness suggest the landslide deposit extends significantly farther east (source-ward) relative to previous mapping. In this eastern portion the landslide deposit is dominantly mantled by younger alluvium. Based on the new mapping the landslide deposit covers up to 22 km2. Cosmogenic samples to directly date landslide emplacement are still being analyzed but tephra layers low in the section underlying the landslide deposit are tentatively correlated with the 11.93±0.03 Ma Ibex Hollow and 11.80±0.04 Ibex Peak 8 ashes, thus providing a Middle Miocene maximum emplacement age.

The remainder of the Spruce Well quadrangle is dominated by Miocene volcanic and sedimentary rocks of the Humboldt Formation and Quaternary alluvial and lacustrine units. Volcanic strata are exposed in the western portion of the area and include poorly consolidated ash-fall tuff, lapilli tuff, and tephra, locally modified by fluvio-lacustrine processes, tentatively grouped with the Blanchard member of the Humboldt Formation. Quaternary units include several alluvial fans and beach bars and playa deposits of pluvial Lake Franklin. This study has yielded new insights into the timing and extent of the Spruce Mountain landslide, and methods used here will be useful in analysis of other similar deposits.

Geological Society of America Abstracts with Programs. Vol. 57, No. 6

doi: 10.1130/abs/2025AM-412482

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