Geologic map of the central part of the San Francisco Volcanic Field, north-central Arizona

The geologic map of the central part of the San Francisco volcanic field (called the Central map area) is one of five adjoining geologic maps (fig. 1) prepared under the Geothermal Research Program of the U.S. Geological Sruvey as a basis for interpreting the history of magmatic activity in the volcanic field. The San Francisco field, which is largely Pliocene and Pleistocene in age, is in northern Arizona, just north of the broad transition zone between the Colorado Plateau. The Central map area encompasses approximately 1,600 km². It spans the middle part of the San Francisco volcanic field and includes some of the oldest and youngest volcanic units in the volcanic field.