Pre-Cretaceous basement rocks and their bearing on large-scale displacements in the San Andreas fault system

Abstract

Investigations of the history of the pre-Cretaceous crystalline rocks of the Transverse Ranges have indicated a complex history from Permo-Triassic times back to 1700 million years or more. Some of the major historical elements are known to be shared with much larger regions in the southwest; others appear unique to the area, at this time. The close juxtaposition to each other and to the San Andreas fault zone of diverse plutonic and metamorphic rocks of widely different ages provides important possibilities for contributing to the nature and history of displacement on the zone. The most effective evaluation will be possible when the crystalline rocks close to the San Andreas fault can be correctly placed into the regional "basement" patterns and history. Unfortunately, the necessary field and laboratory investigations are proceeding very slowly.