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Villa Creek-Estero Bay Melange Outcrops

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Franciscan melanges and ophiolite sections on this stretch of exposed coast are of considerable importance in interpreting the geological history of California and North America. The melange is a chaotic mixture of blocks of several materials im­bedded in a highly sheared shaly matrix; chert and graywacke blocks are common and form a sharp contrast to the marine terraces. The ophiolites are primarily of red chert and metabasic volcanic rock.

According to current theory, melanges are the result of gravity sliding, and these at this site are the result of the Franciscan rocks moving down into an oceanic trench which once bordered North America, before the continent overrode it in the Mesozoic. Ophiolites are emplaced at a mid-ocean ridge on the deep ocean floor.

Integrity: There are several dirt roads in the area, but no development.

Use: On tidelands, research, observation, educa­tion; on private holdings, none.

Ref: Hsu, K. J. 1969. Preliminary Report and Geologic Guide to Franciscan Melanges of the motto Bay-San Simeon Area, California. California Divi­sion of Mines Geol. Spec. Publ. No. 35, 46 pp.

July 1975

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Last modified: December 06, 2005