Many geologic faults have been mapped previously around the Villa Park area, northern Santa Ana Mountains, the longest and perhaps dominant being the El Modeno fault. The trace of this normal fault was mostly inferred to trend northward south of Villa Park, veer to the west in Villa Park, and then to enter the Los Angeles Basin and possibly connect with the Norwalk fault. The Peralta Hills, just north of Villa Park, were presumed to have been formed as a result of vertical movement along the west-trending portion of the fault. The objective of the present study was to better locate the trace of the fault, in particular to determine whether or not it turns west in Villa Park. The locale was a considerable challenge since the few outcrops present during the original mapping are now covered by residential development and the entire area has been urbanized so that access is severely restricted. Seismic refraction was used and the interpretations indicate that the El Modeno fault does not veer west. Rather, it apparently continues a northward trend toward the Peralta Hills and the area is underlain by several north-trending faults.

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