Regional Geophysics and Geology
This section contains 16 chapters that examine the regional geophysics and geology of the province, beginning with a look at the physiography of the borderland west of the peninsula from the mouth of the Gulf to southern California. The fault-produced primary structures have numerous volcanoes and seamounts superimposed on them (LONSDALE). This is followed by a pair of chapters that examine in detail the morphology and fault systems of the inner borderland of northern Baja and southern California. Based on seabeam and detailed geophysical surveys, the inner borderland is an active part of the present-day Pacific-North American plate boundary based on historical seismic activity in the region (LEGG et al. and LEGG). The rocks and sediment sequences for the borderland are placed in a stratigraphic framework by TENG and GORSLINE. They present a preliminary interbasinal stratigraphic correlation for the basins offshore southern California.
The new Bouguer gravity anomaly map for northwestern Mexico is presented; it incorporates approximately 15,000 new measurements for northwestern Mexico (SCHELLHORN et al.). Some of the largest gradients of Bouguer gravity exist in Mexico.
Two chapters focus on the tectonic history of the opening of the Gulf of California. HUMPHREYS and WELDON propose a model for the rifting of the Baja peninsula from the mainland and suggest that additional motion southeast of the mouth of the gulf is required to satisfy the most recent global plate motion solutions. LYLE and NESS present three alternative models for the opening of the southern gulf, based on magnetic anomaly patterns