Geological and Geophysical Maps
Five chapters are included in this section that describe the maps produced for this volume. The maps are all at the same scale; each map is made up of two plates representing a north and a south sheet that can be spliced together. The first chapter (DAUPHIN and NESS) describes a new bathymetric map produced for the area. COUCH et al. discuss the gravity anomaly map that portrays Bouguer anomalies on land and free-air anomalies at sea. This chapter also discusses modeled geophysical sections. NESS et al. compiled a regional map of magnetic anomalies and oceanic crustal isochrons. Spreading rates between the various plates in the region are discussed. Based on magnetic anomaly profiles, a spreading rate, for the mouth of the Gulf of California, of 66 km/My or 49 km/My can be argued equally well. It is hoped that satellite geodetic techniques, discussed in another section of this volume, will resolve this ambiguity in the near future. A seismo-tectonic map (NESS and LYLE) for the marine portion of the province shows the principal faults and lineaments in the area. This map also contains earthquake epicenters (Mb > 4.2) occurring between 1963 and 1985. A new geologic-tectonic map for the entire province, marine and land, was prepared by FENBY and GASTIL. They have partitioned the area into 22 structural domains and the geological history of the region into four major time periods.