This paper discusses the geology of an area of about 150 square miles, extending north and northeast from the town of Mapimí, in north-eastern Durango, Mexico. The location is shown by Figure 1. The area contains an abundance of both intrusive and extrusive igneous rocks and affords an opportunity to correlate part of the igneous geology of north-central Mexico with the stratigraphic and structural problems which have been studied in adjacent areas by Lewis B. Kellum and his associates. In its broader structural relations, the Mapimí district is approximately 25 miles southwest of the Jurassic landmass, first described by Böse,1 which lies within the “belt of intensive deformation which extends . . . from eastern Durango . . . to central Nuevo Leon,” outlined by Kellum, Imlay, and Kane.2
The areal geology is shown on Plate 5, a reconnaissance map, made by a combination of plane-table, car, and pace . . .