Contact Metamorphism at Crestmore, California

Abstract

The Crestmore limestone mine and quarries of the Riverside Cement Company, located 3 miles north of Riverside, California, have received much attention during the past four decades from mineralogists and petrologists the world over, principally because of the occurrence there of a great variety of contact-metamorphic minerals. Most of the 20 or more published accounts dealing with the Crestmore deposits have been concerned primarily with description of the minerals and discussion of their paragenesis. The present paper is a preliminary and condensed version, mainly descriptive, of the results of a study aimed primarily at defining the occurrence and genesis of the minerals and rocks. The contact zones lie between magnesian limestones and quartz diorite, and between the same limestones and a relatively small intrusive mass of quartz monzonite porphyry. The limestones occur as lenses of variable thickness and lateral extent within a thick section of predominantly siliceous metamorphic rocks, masses of which occur typically as roof pendants or screens in the intrusive rocks of the southern California batholith. The younger rocks of this composite batholith have been dated tentatively as Upper Cretaceous, and hence the engulfed metamorphic rocks, which in this area have yielded no fossils, are Mesozoic or older.