- Usage in publication:
-
- Thorn Ranch Tuff*
- Modifications:
-
- Named
- Dominant lithology:
-
- Tuff
- AAPG geologic province:
-
- Denver basin
Summary:
Named for exposures along mesa near Thorn Ranch, at S1/2 sec 23 and N1/2 sec 26, T17S, R73W, Fremont Co, CO in the Denver basin. Is a simple-cooling unit of non-welded to moderately welded tuff that weathers pinkish white to reddish brown depending on degree of welding. Contains pink and white pumice, Precambrian lithic fragments, and brown aphanitic accessory lithic fragments. Is rhyolitic. Contains sanidine, plagioclase, quartz, and biotite as the important phenocrysts. Forms prominent reddish-brown caprock with well developed columnar-jointing. Is 245 ft thick at north end of Echo Park. Occurs from Badger Creek valley west of Black Mountain southeastward through Waugh Mountain and Tallahassee Creek area, and as far south as Goat Creek in northern Wet Mountain Valley. Is younger than East Gulch Tuff and older than Gribbles Park. Exhibits reverse polarity. Its source is unknown. Assigned to the 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 ([ ]).