Recency of rupture, on the other hand, was relatively difficult to isolate. Many of the reports relied on the groundwork laid by a regional fault investigation conducted by Leighton and Associates in 1985. Very little additional information was included, except that a fault trace was found, and it was part of the Pelican Hill fault zone, so it must be inactive. (The Leighton report speculated that the most recent rupture was more than 18,000 years B.P.) I chose to include additional inferences including the type of rock unit or soil horizon ruptured. Rock units of Holocene or Late Pleistocene age are of particular interest.

Leighton and Associates Pelican Hill Fault Investigation (1985):

Offset Marine Terrace deposits (Late Pleistocene)

Date estimated by last major period of glaciation - 18,000 to 20,000 yrs B.P. Low in sea level, much erosion, left stone line (eroded soil away). Fault goes through the stone line, but does not offset the slopewash deposits above it. ìThe cumulative time to form a basal stone line, a weak cambic soil horizon and two additional slopewash units is uncertain.î