The August 1, 1975, Oroville, California, earthquake (Mb = 5.7) and its aftershocks focused considerable interest on current tectonic processes operating in the western foothills of the Sierra Nevada range. As part of an intensive study of this earthquake sequence, the United States Geological Survey with support from the California Department of Water Resources conducted a seismic refraction experiment during July 1976 in the Oroville region. The objective of the experiment is to resolve more clearly the P- and S-wave velocity structure of the crust in the region as a basis for both more accurate hypocenter locations and evidence on the physical properties at depth within the crust.