EVIDENCE OF POSSIBLE LATE QUATERNARY DISPLACEMENT ALONG THE CHUPINES FAULT, MONTEREY COUNTY, CALIFORNIA

During a recent geological investigation south of the intersection of Boots Road and State Highway 68 in Monterey County, California an exploratory trench, excavated approximately 3 meters deep, revealed evidence for late Quaternary movement along the Chupines fault. The trench was located along the mapped trace of the Chupines fault approximately 0.5km south of highway 68 along the top of a ridge. Rocks of the unnamed Pliocene-Pleistocene continental deposits were previously mapped on both sides of the fault at the location of the exploratory trench. The Chupines fault was observed in the trench displacing different lithologies of the unnamed Pliocene-Pleistocene continental deposits. The fault was observed to having an approximate orientation of N60E 45W with a nonindurated, friable, white to light gray sandstone in the apparent hanging wall and a massive bedded, moderately weathered, highly fractured, moderately indurated, medium-grained argillaceous light brown to buff sandstone in the apparent footwall. The soil profile above the continental deposits is relatively thin (less than 20 cm) and vaguely appears to have been displaced by the fault.

The Chupines fault is a northwest trending, northeast dipping reverse fault. Many other similar faults in the Monterey area are subparallel to the Chupines fault and also show apparent reverse movement. However none of these faults are considered active by the State of California Alquist-Priolo earthquake fault zone act. The data obtained from this study should be considered for future decisions of public policy regarding the activity of the Chupines and other associated faults in the Monterey area.