The nature of the Sierra Nevada is amazing not only on the surface but also beneath it. Mountains generally have a thick crust underneath them and the lack of a thick crustal root underneath the Sierra Nevada reported by previous geophysical studies still needs to be resolved. The general crustal structure of the southern Sierra Nevada and surrounding area was examined by author through the analysis of gravity and magnetic data. A series of Bouguer gravity, low-pass and band-pass wavelength filtered gravity and reduced to the pole total magnetic intensity maps were produced to define the general tectonic features of the study area. Two regional gravity models were utilized for determining the general crustal structure of the region and the location of the denser upper mantle body under the Great Valley and the Sierra Nevada region. This gravity analysis study provides additional information to help explain a lack of thick root beneath the Sierra Nevada.