Chronology and deformation of Quaternary marine shorelines, San Diego County, California

A series of 16 marine terraces and associated landforms and sedimentary deposits provides a record of Quaternary paleogeographic and tectonic history of coastal San Diego County, California. The width of individual terrace platforms varies dramatically, from several kilometers in places where the platforms are cut into poorly lithified sedimentary strata, to a few meters or tens of meters where the platforms are cut in more resistant rocks. Beach ridges formed of dune sands lie just landward of most of the terrace shorelines. Radiometric ages and amino-acid racemization ratios, together with shoreline elevations, have been used to calculate average rate of uplift and to construct a chronology of the 16 shorelines, which range in age from 80 ka to perhaps as old as 1.29 ma. Shoreline-angle elevations suggest that nearly the entire length of coastal San Diego County has been uplifted at a rate of 0.13 to 0.14 m/ka during the Quaternary. Both higher and lower rates are recorded in areas deformed by the Rose Canyon fault zone. Changes in configuration of successive shorelines indicate that rocks on one side of the fault have been rising through middle and late Quaternary time and that the Rose Canyon fault has been active for at least the past 1 my.