There are two competing models for the mesozoic tectonic history of southern California - closure of a marginal basin between North America and an outboard continental fragment and normal oceanic subduction under North America. The Pelona- Orocopia-Rand-Portal Ridge schists and the Vincent-Chocolate Mountains-Orocopia- Rand thrust faults are products of this tectonic episode. This study will attempt to resolve this issue by close examination of the thrust fault in the Gavilan Hills where the clear-cut northeast vergence forms the main argument for the marginal basin model. The work will test the possibility that the northeast motion is due to a younger normal fault which re-activated the original thrust. Results are applicable to the resolution of Mesozoic tectonics in the southwestern United States.
