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Southern California Geology

Geologic Setting of the San Gabriel Mountains, Transverse Ranges Province

Geologic Structures

Cucamonga Fault Zone

The Cucamonga Fault zone is located along the southern margin of the eastern San Gabriel Mountains, and marks the eastern end of the frontal-fault system of the San Gabriel Mountains. The fault zone consists of numerous inter-twining, east-striking, north-dipping thrusts that separate crystalline basement rocks of the eastern San Gabriel Mountains from alluvium of upper Santa Ana valley to the south. Some thrust faults of the zone lie entirely within alluvium (Morton and Matti, 1987). Slickensides in the basement rocks are consistently oriented down-dip, indicating the most recent displacements along the Cucamonga Fault zone have been pure thrust.

Faulting has occurred throughout the Quaternary, with individual faulting events estimated at about 6.7 M with a recurrence of about 625 years for the past 13,000 years (Matti and others, 1982; Morton and Matti, 1987). The average north-south convergence across the Cucamonga Fault zone is estimated to have been in the range of 3 mm/yr (Weldon, 1986) to 5 mm/yr (Matti and others, 1982b; Morton and Matti, 1987).

Continue to Geologic Structures, San Gabriel Fault
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