Ingleside chert. Name proposed for 2nd from uppermost formation of Franciscan Group. Occurs on San Francisco Peninsula and in Marin County, California. Consists of radiolarian chert of prevailingly dull brownish red color especially in its thicker and more evenly bedded portions but also includes some yellow and green rock and locally rock of other colors. Contains thousands of thin beds of earthy shale. In many places rock is true jasper. Maximum thickness about 530 feet. Overlies Marin sandstone (new); underlies Bonita sandstone (new) (both of Franciscan group). Age is Jurassic(?).
Named from exposures in San Miguel Hills, east of town of Ingleside, San Francisco 15-min quadrangle, San Francisco Co., CA.
[Discrepancy: GNU records (USGS DDS-6; Menlo GNULEX) state unit is "named for exposures in Ingleside, San Miguel Hills ..." --unresolved.]

Source: US geologic names lexicon (USGS Bull. 896, p. 1013-1014); GNU records (USGS DDS-6; Menlo GNULEX).

Ingleside Chert of Franciscan Group of Lawson (1914), later Ingleside Chert 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).