A series of 12 paleotectonic maps and 5 paleogeologic maps presents the major stages of the evolution of the central and western part of the continent from early Paleozoic to late Mesozoic. They cover the western Cordillera from central British Columbia and Alberta, south to central Mexico, the central stable region east to Lake Michigan, and the Mid-Continent and part of the Gulf region. The tectonic maps show for each period or partial period of time: (1) the belts of severe compression and igneous activity; (2) the regions of epeirogenic uplift that were subjected to erosion; (3) the areas which received less than 1,000 feet of sediments; and (4) the basins and troughs which subsided and received more than 1,000 feet of sediments. The basins and troughs, where possible are contoured on 1,000-foot intervals. In summary, the tectonic maps show the crustal movements for each period. Tectonic elements are emphasized whereas the paleogeographic map emphasizes shore lines, and commonly obscures the tectonic elements.

The series of paleogeologic maps starts with the outcrop pattern of the continent at the close of the Devonian, and presents views of its developing complexity at the close of the Lower Pennsylvanian, the Permian, the Triassic, and the Jurassic. Both the tectonic and geologic maps seem necessary to gain an adequate understanding of the major geologic elements of the continent and the way they evolved.

In some areas much detail had to be generalized; in others, hazardous interpretations had to be drawn. The purpose is to present the maps as preliminary copies, and to ask for assistance in correcting and adding to the data they show.