Significant Earthquakes and Faults
Fault Name Index
Clamshell - Sawpit Canyon Fault
Type of Fault: reverse
Length: 18 km
Nearby Communities: Sierra Madre, Monrovia
Most Recent Surface Rupture: Late Quaternary
Other Notes: This fault dips to the north at about 40 (at the surface) to 50 (at depth) degrees.
The Sierra Madre earthquake of 1991 probably originated on the Clamshell - Sawpit Canyon fault. Though a sizable earthquake, the depth of this quake prevented the rupture from reaching the surface.