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.