RESEARCH· ·1970·

GE·OLOGICAL SURVEY RESEA·RCH 1970
AEROMAGNETIC AND GRAVITY FEATURES OF THE WESTERN FRANCISCAN
AND SALINIAN BASEMENT TERRANES BETWEEN CAPE SAN MARTIN
AND SAN LUIS OBISPO, CALIFORNIA
By W. F. HANNA, Menlo Park, Calif.
A.bstract.-Aeromagnetic and gravity data covering a 30- by
65-mile area along the southwest coast of California help delineate
the occurrence of subsurface serpentinites, plutonic and
metamorphic rocks, and sedimentary basin fill within the eugeosynclinal
Franciscan and the plutonic and metamorphic Salinian
basement complexes. The magnetic data suggest that the
buried contact between basement tracts forms a broad arc, convex
toward .,.the northeast, between the exposed basement contacts
in the northern and southern parts of the area. Gravity
data conspicuously reflect thick sedimentary rock accumulations
within each of the basement terranes. ·
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Saliriian basement
l'fKtoftic and mdamorplic comple:t
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Franciscan
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