The National Geologic Map Database is migrating to a new infrastructure. We apologize for any service disruptions during this process.

U.S. Geological Survey Home AASG Logo USGS HOME CONTACT USGS SEARCH USGS
National Geologic Map Database
Map showing publication footprint
  • Usage in publication:
    • Chalk Mountain Rhyolite*
  • Modifications:
    • Age modified
  • AAPG geologic province:
    • Eagle basin
Publication:

Tweto, Ogden, 1974, Geologic map and sections of the Holy Cross quadrangle, Eagle, Lake, Pitkin, and Summit Counties, Colorado: U.S. Geological Survey Miscellaneous Investigations Series Map, I-830, 2 sheets, scale 1:24,000


Summary:

Occurs 2 mi east of this quad in Summit Co, CO in the Eagle basin. Correlated with a map unit called "rhyolite porphyry (Trp)." Has a radiometric age (K-Ar) of 29 m.y. Age, therefore, changed from Eocene to Oligocene.

Source: GNU records (USGS DDS-6; Denver GNULEX).


For more information, please contact Nancy Stamm, Geologic Names Committee Secretary.

Asterisk (*) indicates published by U.S. Geological Survey authors.

"No current usage" (†) implies that a name has been abandoned or has fallen into disuse. Former usage and, if known, replacement name given in parentheses ( ).

Slash (/) indicates name conflicts with nomenclatural guidelines (CSN, 1933; ACSN, 1961, 1970; NACSN, 1983, 2005, 2021). May be explained within brackets ([ ]).

Accessibility FOIA Privacy Policies and Notices

USA Gov U.S. Department of the Interior | U.S. Geological Survey
Supported by the National Cooperative Geologic Mapping Program
Page Contact Information: Personnel
Page Last Modified: Thu 21 May 2026 05:37:23 PM MDT