Pervasive Neogene extension approaching 100% in SW North America produced a suite of metamorphic core complexes. Core complexes form as rocks ascend from the middle crust along extensional, low-angle detachment faults. This illustration by Jon Spencer (AZGS retired) displays the distribution of core-complexes and their association with detachment faults and mylonitic rocks in northern Mexico, Arizona and eastern-most California.
Spencer, J.E., 2006, A geologist's guide to the core complex geology along the Catalina Highway, Tucson Area, Arizona. Arizona Geological Survey Open File Report, OFR-06-01, 38 p http://repository.azgs.az.gov/uri_gin/azgs/dlio/360
Dickinson, William R., 1992, Geologic Map of Catalina Core Complex and San Pedro Trough: Arizona Geological Survey Contributed Map CM-92-C, map scale 1:125,000, 1 map sheet. http://repository.azgs.az.gov/uri_gin/azgs/dlio/1520
Reynolds, S.J., 1985, Geology of the South Mountains, Central Arizona. Arizona Geological Survey Bulletin-195, 75 p., 1 map plate, scale 1:24,000. http://repository.azgs.az.gov/uri_gin/azgs/dlio/1655