Trench Log

Trench log (a) and photograph (b) of exposure on the northeast side of the pressure ridge (trench 3, southeast wall, in perspective view). Faults, in red; ground surface at the time of the most recent earthquake, in gold. Labeled triangles on trench log mark locations of charcoal samples collected for radiocarbon analysis. These radiocarbon dates indicate that the most recent earthquake occurred after A.D. 1690 AD and most likely after A.D. 1715. The absence of accounts of a large, damaging earthquake in the early historical record implies that this earthquake occurred before Mission Dolores was founded in San Francisco in A.D. 1776.