Stratigraphy and Geologic Structure of Uppermost Cretaceous and Tertiary Rocks of the East-Central Part of the San Juan Basin, New Mexico

An area of about 1,300 square miles was mapped in parts of Rio Arriba, Sandoval, and McKinley Counties, New Mexico. The area is in the east-central part of the San Juan Basin, a large structural and drainage basin in the east-central part of the Colorado Plateau province. Six relatively distinct physiographic sectors in the area are named here: the Penistaja Cuestas; Largo Plains; Tapicitos Plateau; Yeguas Mesas; San Pedro Foothills; and Northern Hogback Belt. The mapped area lies in the Central basin of the San Juan Basin and is bounded on the east by the Nacimiento and French Mesa-Gallina uplifts where rocks ranging in age from Precambrian to Late Cretaceous crop out. Upper Cretaceous rocks crop out along the southern and eastern ridges of the area, and Tertiary rocks are at the surface in most of the area