Radiometric Ages of Volcanic Rocks on the Fort Rock Dome and in the Aquarius Mountains, Yavapai and Mohave Counties, Arizona

Open-File Report 2019-1038
By: , and 



The Fort Rock dome, in Yavapai County, Ariz., is a roughly circular geologic structure in plan view, 2.5 km in diameter, that is similar in many ways to an impact crater; however, it is a structural dome caused by a potassic mafic intrusion at depth, and the crater-like depression in its center is erosional in origin. The Aquarius Mountains, west of the Fort Rock dome, in Mohave County, contain a felsic volcanic center that erupted tuffs, non-welded ash-flow tuffs, and lahars following dome emplacement.

This report discusses the radiometric ages of samples of rock units from both the Fort Rock dome and the Aquarius Mountains eruptive center. The ages for all samples span a short interval of time from 22.3 to 21.7 m.y. (earliest Miocene). The individual sample ages are consistent with the stratigraphic order of the rock units in the area, and the short age span is consistent with the absence of any significant unconformities in the section.

Suggested Citation

Fuis, G.S., Calvert, A., and Sullivan, K., 2019, Radiometric ages of volcanic rocks on the Fort Rock dome and in the Aquarius Mountains, Yavapai and Mohave counties, Arizona: U.S. Geological Survey Open-File Report 2019–1038, 18 p.,

ISSN: 2331-1258 (online)

Study Area

Table of Contents

  • Abstract
  • Introduction
  • Geologic Setting
  • Sample Description
  • Radiometric Dating Method
  • Dating Results
  • Discussion
  • Summary
  • Acknowledgments
  • References Cited

Additional publication details

Publication type Report
Publication Subtype USGS Numbered Series
Title Radiometric ages of volcanic rocks on the fort rock dome and in the aquarius mountains, Yavapai and Mohave Counties, Arizona
Series title Open-File Report
Series number 2019-1038
DOI 10.3133/ofr20191038
Year Published 2019
Language English
Publisher U.S. Geological Survey
Publisher location Reston, VA
Contributing office(s) Earthquake Science Center
Description iv, 18 p.
Country United States
State Arizona
County Yavapai County, Mohave County
Online Only (Y/N) Y
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