O'Leary Peak is an extinct lava-dome volcano in northern Arizona within the San Francisco volcanic field north of Flagstaff and northwest of Sunset Crater National Monument. Reaching 8,919 feet, it stands among the higher summits in this volcanic landscape. Dating to the Pleistocene, it preserves evidence of the volcanic activity that shaped much of the area around Flagstaff. A fire lookout tower built later on a subsidiary eastern peak connected the mountain's ancient geologic origins with a practical role overseeing the surrounding forested high country.