The goal of this research project is to investigate the geochemistry, isotope geology, age, and tectonic significance of mafic intrusive rocks in the Sierra Nevada, White Mountains, Inyo Mountains, and Mojave Desert. The proposed research will include a study of the widespread Independence dike swarm as a coeval intrusive suite which crosses several tectonic boundaries. Field mapping, major-, trace-element and isotopic analyses, Sr, Nd, and Pb isotopic analyses, and U-Pb age determinations of rock suites should provide constraints on the nature of the mantle that generated the batholithic magmas in California and data to test various models for the tectonic evolution of the southwestern United States.