9417901 Reynolds This project is an interdisciplinary study of the Cenozoic evolution of the crust and lithosphere across the Colorado, Plateau-Basin and Range boundary. Lateral changes in crustal and lithospheric thickness across this major tectonic boundary, and their relationship to the extension of continental crust, will be assessed. Two transects will be studied by: geologic mapping and structural geology; sedimentological, stratigraphic and fission track analysis; and volcanic, petrologic and geochemical analyses. The results will provide insight into continental extensional processes and will have direct relevance to many other extensional tectonic regimes elsewhere.