PLEASE NOTE: the maps on this page are no longer updated or revised. Any revisions to the series are available at
The database for the images consists of many papers published on the geology of SW NAM. My own work is incorporated onto the Colorado Plateau portion of the maps. Plate patterns are from PGIS MAC, a plate-tectonic computer program by the Paleomap Project. Major sources of data are listed below:
BLAKEY, Ronald C., Dept of Geology, Northern Arizona Univ, Box 4099, Flagstaff AZ 86011, email@example.com
The early Mesozoic was a time of great change for southwestern North America (NAM) as the continental margin evolved from chiefly passive during most of the Paleozoic to active in the early Mesozoic. This fundamental tectonic evolution produced dramatic changes in the paleogeography of the region from passive-margin coastal plains to active-margin mountains, arcs, and tectonic basins. A series of shaded-relief paleogeographic maps have been prepared to visually emphasize these changes. These maps were constructed using tectonic, stratigraphic, and sedimentologic data. Although consensus of geologic interpretation is rare in this complex region, certain basic inferences can be made regarding gross paleogeography. This results in general trends in the distribution of major landforms, both structural and depositional. For the Colorado Plateau region, rather detailed paleogeomorphic maps can be prepared and the resolution of the maps is less than the detail of the known geology. For the Cordilleran region, the detail shown on the maps is more hypothetical and the detail shown exceeds the geologic resolution. This is particularly true of terranes that have had great lateral transposition since their initial formation and deformation.
The change from passive to active margin was not sudden, but rather evolved as a series of oceanic arcs approached and collapsed against NAM. As the Cordilleran margin was built, it developed as continental (Andean) to the south and marine to the north. The marine arc collapsed against NAM by Late Jurassic and an Andean arc was established across the region. These broad trends were punctuated by accretion of exotic microplates, some of which produced local to regional mountain building. Additional complications to the paleogeography were created by transverse motions of small and large plates along the Cordilleran margin. Until the history of these blocks becomes better understood, the details of the paleogeography will remain tentative.