Crustal thickness of the peninsular ranges and gulf extensional province in the Californias

We estimate crustal thickness along an east-west transect of the Baja Calif ornia peninsula and Gulf of California, Mexico, and investigate its relatio nship to surface elevation and crustal extension. We derive Moho depth esti mates from P-to-S converted phases identified on teleseismic recordings at 11 temporary broadband seismic stations deployed at similar to 31 degreesN latitude. Depth to the Moho is similar to 33 (+/-3) km near the Pacific coa st of Baja California and increases gradually toward the east, reaching a m aximum depth of similar to 40 (+/-4) km beneath the western part of the Pen insular Ranges batholith, The crust then thins rapidly under the topographi cally high eastern Peninsular Ranges and across the Main Gulf Escarpment, C rustal thickness is similar to 15-18 (+/-2) km within and on the margins of the Gulf of California. The Moho shallowing beneath the eastern Peninsular Ranges represents an average apparent westward dip of similar to 25 degree s. This range of Moho depths within the Peninsula Ranges, as well as the sh arp similar to east-west gradient in depth in the eastern part of the range , is in agreement with earlier observations from north of the international border. The Moho depth variations do not correlate with topography of the eastern batholith, These findings suggest that a steeply dipping Moho is a regional feature beneath the eastern Peninsular Ranges and that a local Air y crustal root does not support the highest elevations. We suggest that Moh o shallowing under the eastern Peninsular Ranges reflects extensional defor mation of the lower crust in response to adjacent rifting of the Gulf Exten sional Province that commenced in the late Cenozoic, Support of the eastern Peninsular Ranges topography may be achieved through a combination of flex ural support and lateral density variations in the crust and/or upper mantl e.