- Usage in publication:
-
- Cahil sandstone*
- Modifications:
-
- Named
- Dominant lithology:
-
- Sandstone
- Limestone
- Chert
- AAPG geologic province:
-
- California Coast Ranges province
Summary:
Named as lowermost formation in Franciscan group for Cahil Ridge in San Mateo 15' quad, San Mateo Co, CA. Includes Calera limestone member (new). Is prevailingly massive, obscurely bedded sandstone of dark greenish-gray color and medium texture. Includes lenses of limestone and chert. Is approximately 2560 ft thick, made up of about 60 ft of Calera limestone with 500 ft of sandstone below and 2000 ft of sandstone above Calera. Underlies Sausalito chert (new) of Franciscan group. Intruded by basalt and diabase. Age given as Jurassic(?).
Source: GNU records (USGS DDS-6; Menlo GNULEX).
- Usage in publication:
-
- Cahil Sandstone, Memberâ€
- Modifications:
-
- Abandoned
- AAPG geologic province:
-
- California Coast Ranges province
Summary:
Cahil Sandstone of Franciscan Group of Lawson (1914), later Cahil Sandstone Member of Franciscan Formation, is abandoned because writer was unable to use beds as stratigraphic markers as suggested by Lawson. Age of Franciscan is Jurassic and Cretaceous based in part on single ammonite DOUVILLEICERAS sp. (Schlocker and others, 1954).
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 ([ ]).