Cenozoic Geology of Fort Irwin and Vicinity, California

Open-File Report 2013-1024- C
Prepared in cooperation with the U.S. Army, Fort Irwin National Training Center
By: , and 
Edited by: David C. Buesch



The geology of the Fort Irwin National Training Center in the north-central Mojave Desert, California, provides insights into the hydrology and water resources of the area. The Fort Irwin area is underlain by rocks ranging in age from Proterozoic to Quaternary that have been deformed by faults as young as Quaternary. Pre-Tertiary sedimentary, igneous, and metamorphic bedrock and Miocene volcanic and sedimentary rocks are exposed in the mountains and ridges, between which are basins containing Quaternary to Pliocene deposits. During the Miocene, in the western part of Fort Irwin, development of the Eagle Crags volcanic field resulted in a complex assemblage of lava flows, pyroclastic flow and fallout tephra deposits, and volcaniclastic sedimentary rocks that were deposited in alluvial, fluvial, and locally lacustrine environments; in the eastern part of Fort Irwin, epiclastic sedimentary rocks and minor tuffaceous rocks were deposited in alluvial, fluvial, and locally lacustrine environments. In the Pliocene and Quaternary, sandstone and conglomerate were deposited in alluvial and fluvial environments, and locally fine-grained materials were deposited in lacustrine, eolian, playa, and groundwater discharge environments. The Fort Irwin area is transected by Neogene to Holocene northwest- and east-striking (and fewer northeast-striking) strike-slip, normal, and locally thrust faults. Structural blocks between faults are broadly warped, and locally rocks adjacent to the faults are folded and sheared. Many of these faults influenced the formation or modification of basins, especially after about 11 million years, when the Eastern California Shear Zone developed in this area. The three-dimensional geologic framework produced by the late Cenozoic stratigraphic and structural history is represented by the continuity or spatial limitations of lithostratigraphic and correlative hydrogeologic properties. The continuity or limitations of rocks and properties influence how water moved (and moves) through the hydrogeologic system.

Suggested Citation

Buesch, D.C., Miller, D.M., and Menges, C.M., 2018, Cenozoic geology of Fort Irwin and vicinity, California, chap. C of Buesch, D.C., ed., Geology and geophysics applied to groundwater hydrology at Fort Irwin, California: U.S. Geological Survey Open-File Report 2013–1024–C, 39 p., https://doi.org/10.3133/ofr20131024C.

ISSN: 2331-1258 (online)

Study Area

Table of Contents

  • Abstract
  • Introduction
  • Methods
  • Lithostratigraphy
  • Faults and Folds
  • Conclusions
  • References Cited

Additional publication details

Publication type Report
Publication Subtype USGS Numbered Series
Title Cenozoic geology of Fort Irwin and vicinity, California
Series title Open-File Report
Series number 2013-1024
Chapter C
DOI 10.3133/ofr20131024C
Year Published 2018
Language English
Publisher U.S. Geological Survey
Publisher location Reston, VA
Contributing office(s) Geology, Minerals, Energy, and Geophysics Science Center
Description Report: iv, 39 p.
Larger Work Type Report
Larger Work Subtype USGS Numbered Series
Larger Work Title Geology and geophysics applied to groundwater hydrology at Fort Irwin, California
Country United States
State California
County San Bernardino County
City Fort Irwin
Online Only (Y/N) Y
Additional Online Files (Y/N) N
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