Up close, the fault looks like this. A granodiorite on the south separated from a gneiss on the north by the San Gabriel Fault. Previous workers have estimated that between 40 and 60 kilometers of slip have occurred on this fault zone which is only about 5 cm wide. If youíre looking for an example of a narrow fault zone, this is it.
Weíve analyzed fission track samples from a profile on the south side of the fault.