Bedrock Geologic Map of Sentinel Peak (A-Mountain) and Tumamoc Hill, Pima County, Arizona, v. 1.0

Tumamoc Hill and Sentinel Peak form a group of hills at the western edge of Tucson in southeastern Arizona, and comprise a small part of the Tucson Mountains. Sentinel Peak, also known as A-Mountain, is a prominent landmark near downtown Tucson. The geology of Tumamoc Hill and Sentinel Peak is dominated by 20 to 30 million year old (Ma) volcanic rocks, unlike most of the rest of the Tucson Mountains which are composed primarily of much older volcanic rocks that were largely produced during a single enormous eruption (Lipman, 1993; Kring, 2002). This map is simplified from the map of Phillips (1976, University of Arizona M.S. thesis). It was created so that the geology of the Tumamoc Hill – Sentinel Peak area can be readily discerned from an available color map, and includes a description of map units and their approximate ages. Potassium-argon (K-Ar) radiometric dates are given with 1σ analytical uncertainty, and most dates are recalculated by Reynolds et al. (1986) using newer decay and abundance constants.