Description
The uplift rate on Santa Rosa Island has been determined to range from 0.08-0.17 mm/yr based on field mapping and measurements of elevations of the first three emergent marine terraces on Santa Rosa Island, and the two uranium-thorium dates of solitary corals collected from the second emergent marine terrace near Johnsons Lee. The dates for the coral, Balanophyllia elegans, are 120±3 and 114±4 ka. Based on these dates, the second marine terrace is correlated to terraces formed during oxygen isotope substage Se. Relative to the second marine terrace, the first marine terrace would then probably correlate to the substage 5a high stand, and the third marine terrace would correspond to the stage 7. Using the uplift rate determined for the north coast of the island near Arlington and Tecolote canyons, a high (150-180 m) marine terrace is estimated to be about 0.9-1.1 Ma in age. Based on the 0.9-1.3 km deflection of canyon drainages that incise the high terrace, the approximate long-term slip rate of the Santa Rosa Island fault is 1 mm/yr. The relationship between the Santa Rosa Island fault, the Santa Cruz Island fault, and the Santa Monica fault suggest a minimum left-lateral rate of about 1 mm/yr for the Santa Monica fault near Los Angeles.
