Distribution in Time and Space of Late Phanerozoic Normal Faulting in Nevada and Utah

To understand the timing of extensional deformation which has occurred in the Great Basin since the close of the Sevier orogeny, a compilation of normal fault ages was made for Nevada and western Utah. Available literature indicates that normal faulting occurred there on a regional scale in the Late Mesozoic and Early and Middle Tertiary as well as in the Late Tertiary and Quaternary. There is no apparent spatial pattern in the age of initial normal faulting in Nevada and Utah; apparent areal differences in the intensity of fault development for a given time period may be real or a function of missing stratigraphic units needed to define properly the ages of faulting. Although Late Tertiary and Quaternary normal faults would probably be classified as basinrange faults by most workers, a question remains as to the nature of the Late Mesozoic and Early and Middle Tertiary normal faults. They could represent initial basin-range type extension, or they could represent a distinct episode of extension between the Sevier and "BasinRange" orogenies.