"These craterlets occurred on practically all the saturated alluvial bottoms of the streams within the zone of destructive effects, and also on the tidial mud flats of Tomales Bay" (page 403 of 1908 Lawson and others "Report of the State Earthquake Investigation Commission"). Sand boils like these are an indicator that sand layers beneath the surface liquefied. They aren't necessarily damaging, but may be accompanied by settlement, lateral spreading or other surface deformation that does cause damage. (Photograph by J.C. Branner, Plate 143A in Lawson and others report on the 1906 earthquake, 1908)

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