Sentinel Peak is a 2,897 ft peak in the Tucson Mountains southwest of downtown Tucson, Arizona. The valley's first inhabitants grew crops at the mountain's base, along the Santa Cruz River. The name "Tucson" is derived from the O'odham Cuk Ṣon, meaning " base of the black ". In the 1910s University of Arizona students used local basalt rock to construct a 160-ft-tall block "A" on the mountain's east face, near its summit, giving the peak its other name, "A" Mountain. The peak is part of a 272-acre park, the largest natural resource park in the City of Tucson.Early historyThe fertile land at the base of Sentinel Peak was used for agriculture from circa 2000 BCE until the 1930s. Bedrock mortars found on the sides of the peak are believed to have been used to grind corn and mesquite beans into flour. In the 1690s the O'odham people living in the area were visited by Father Eusebio Francisco Kino, who established the nearby Mission San Xavier del Bac. After Presidio San Augustin del Tucson was constructed in 1775, sentinels were stationed on the peak to watch for raiding Apaches.GeologySentinel Peak is made up of several layers of igneous rock representing various types of volcanic activity, though the mountain itself is not a volcano. It is one of a cluster of outcroppings at the eastern edge of the Tucson Mountains that are primarily the remnants of 20-30 million-year-old (Ma) lava flows that once extended west towards the Tucson Mountains and east into the Tucson Basin, where the city is now. Erosion and faulting are responsible for the peak's conical shape.
