36 Advances in understanding landslides and other mass movements

In this session we want to highlight advances in understanding mass movements, including studies focused on description, mapping, monitoring, triggering mechanisms, mitigation, modeling, and evaluating susceptibility.

Wednesday, 11 March 2026
8:30 AM - 10:30 AM
RCC, 105

Using 36Cl dating to Determine Age of Emplacement of the Spruce Mountain Landslide Deposit in Elko County, NV

Paper number: 36-5
Program: Technical Sessions
Time: 9:35 AM – 9:50 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 to the penultimate glacial period, roughly estimated at 150-200 kya, and the size of the deposit to be significantly larger than previous mapping indicated.  

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 proximal part of the deposit. 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 1-2 meters of landslide breccia is mantled by younger alluvium. Based on the new mapping the landslide deposit covers up to 22 km2. 36Cl-dating samples were collected from limestone breccia at the surface of the landslide deposit and analysis indicates their exposure age to be between 150-200 kya.  

The Spruce Mountain landslide deposit is bisected by a gap of little-to-no landslide material in the center, and remote sensing suggests a north-to-south normal fault may have dropped part of the deposit down, obscuring much of the previously exposed landslide deposit. This is supported by the presence of other normal faults present in the valley and in Spruce Mountain proper. This study has yielded new insights into the timing and extent of the Spruce Mountain landslide, and 36Cl-dating landslide emplacement age is a viable analysis method for other similar deposits.  

Geological Society of America Abstracts with Programs. Vol. 58, No. 1

doi: 10.1130/abs/2026SE-411764

© Copyright 2026 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.