The Flagstaff area, on the southern margin of the Colorado Plateau, offers an exceptional variety of geologic wonders. The landscape of this plateau is composed of remarkable geologic features: the towering, glaciated peaks of San Francisco Mountain, underground lava tubes and blowholes; meteor-blasted Barringer Crater, and cinder cones and lava flows of the San Francisco volcanic field. This booklet is your guide to the geologic features of the fascinating landscape of the Flagstaff area. It is a hiker's guide; walks to the geologic features described in the text are encouraged. This book was written for the visitor who has an interest in geology, but may not have had formal training in the subject. It may also help ensure that the visiting geologist does not overlook some of the features described.