The North American Cordillera contains a number of exotic terranes that were accreted to the continental margin during late Mesozoic to Tertiary time. Study has focused on those Terranes presently found in the northern part of the Cordillera in the Pacific northwest and Canada. One of the largest such Terranes however, is the Guerrero Terrane of western Mexico and is the subject of this project. The Terrane consists of Jurassic- Cretaceous submarine lavas volcaniclastics, and sedimentary rocks. The project will include mapping, isotopic characterization and radiometric age dating. These and other data will be integrated to constrain models of mesozoic paleogeography of the western margin of North America and the role of Guerrero Terrane and its accretion.