- Usage in publication:
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- Johnstone Peak tuff breccia
- Modifications:
-
- Named
- Dominant lithology:
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- Breccia
- AAPG geologic province:
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- Los Angeles basin
- Transverse Ranges province
Summary:
Named as member of Glendora volcanics for Johnstone Peak, San Gabriel Mountains, Los Angeles Co, CA, south of which unit is typically exposed. Occurs at various horizons in Glendora volcanics. Contains numerous scattered subangular fragments and blocks ranging in diameter from fraction of an inch to over 10 ft. In most outcrops deposit is chaotic with no sign of bedding. Total thickness is about 100 to 700 ft. Unit lies between and upon three lava members of Glendora volcanics. High proportion of tuff matrix suggests nuees ardentes eruption. Age of Glendora volcanics shown as middle Miocene or older on map legend.
Source: GNU records (USGS DDS-6; Menlo 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 ([ ]).