Geologic map of the Morena Reservoir 7.5-minute quadrangle, San Diego County, California

Introduction

Mapping in the Morena Reservoir 7.5-minute quadrangle began in 1980, when the Hauser Wilderness Area, which straddles the Morena Reservoir and Barrett Lake quadrangles, was mapped for the U.S. Forest Service. Mapping was completed in 1993–1994. The Morena Reservoir quadrangle contains part of a regional-scale Late Jurassic(?) to Early Cretaceous tectonic suture that coincides with the western limit of Jurassic metagranites in this part of the Peninsular Ranges batholith (PRB). This suture, and a nearly coincident map unit consisting of metamorphosed Cretaceous and Jurassic back-arc basinal volcanic and sedimentary rocks (unit KJvs), mark the boundary between western, predominantly metavolcanic rocks, and eastern, mainly metasedimentary, rocks. The suture is intruded and truncated by the western margin of middle to Late Cretaceous Granite Mountain and La Posta plutons of the eastern zone of the batholith.