Our ideas of thrust-faults have been deduced from observations on dislocations in hard, competent strata, such as are found in the Appalachian Mountains of the United States, in the Highlands of Scotland, or in continental Europe, where the epochs of such faulting are commonly either in the Mesozoic or Paleozoic. In the Coast Range of California, however, the writers have recently observed thrust-faulting in incompetent strata of Tertiary and Quaternary age, and in places the pressures responsible for the faulting are still active. In addition, uplifts in soft Pleistocene sediments are causing extensive slumping, and a combination of faults with zones of slumping produce several striking topographic features. These conditions were discovered in San Benito County, about 75 miles south of the city of San Francisco (see figure 1).
San Benito County is crossed by the San Andreas Fault, along which much movement was observed and recorded at the . . .