The northwestern margin of the Santa Catalina Mountains, located within Catalina State Park and the adjacent Coronado National Forest, contains a variety of spectacular geologic features (Map A). Because of the relatively sparse desert vegetation, all of them are easy to recognize and photograph. Some of these features occur throughout much of the western United States. Others are unique to landscapes produced by the weathering and erosion of granite. This booklet is your field guide to the geology of this splendid desert landscape. It is a hiker’s guide; excursions on foot to the geologic features described in the text are encouraged. This book is 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. To set the stage, I have briefly described the area’s geologic setting and geologic history. In the following pages, emphasis is given to descriptions of geologic features that are common in this landscape. Precise locations are provided for those features that have more limited distribution. Includes more than 30 images and illustrations and six maps.