Gravity survey in southern Cascade Range, California
A regional gravity survey in the southern Cascade Range and environs was made during the summers of 1962 and 1963. Twelve hundred gravity stations were established within the area enclosed by lat 41°00'N, lat 42°301N, long 120°00'W, and long 124°00'W. Most of the stations are concentrated in an area overlapping the axis of the High Cascades in the vicinity of Mount Shasta. An average station density of one station in 7 square miles was obtained. A Bouguer-anomaly gravity map has been made of the area by standard methods. The major gravity feature is a .100-mgal eastward decrease across the Klamath Mountain-Cascade Range contact. A residual negative anomaly of about 35 mgal is associated with the Cascade volcanic rocks and a residual positive anomaly of about 40 mgal is associated with the Klamath Mountain rocks. A preliminary interpretation suggests a regionally-compensated crust beneath the Interior Platform (a large volcanic plateau) and a net mass excess in the crust beneath the Klamath Mountains (a region of crustal shortening). Depth estimates suggest that the disturbing masses are, at least in part, relatively shallow in the earth's crust. Under Shasta Valley the top surface of the disturbing mass must be within the upper 10 km.