Within the San Andreas Fault transform system, geomorphic structures of transtension, such as pull-apart basins and offshore grabens, are evidence of subsidence between transform faults, as well as areas of normal faulting.
Just offshore of the Marin County coast the prominent marine San Andreas Graben lays snuggly between submerged arms of the San Andreas and Golden Gate Faults. This deep, submerged pull apart basin is adjacent to the epicenter of the 1906 San Francisco Earthquake, and indicates major transtensional forces are at play along this famous stretch of the San Andreas system.
