Sentinel Peak (Arizona)

From Wikipedia, the free encyclopedia
Jump to: navigation, search
Sentinel Peak
"A" Mountain
Picture of the "A" on Sentinel Peak
Elevation 2,901 ft (884 m) NAVD 88[1]
Location Tucson, Pima County, Arizona, U.S.
Range Tucson Mountains
Coordinates 32°12′37″N 110°59′32″W / 32.2103°N 110.9923°W / 32.2103; -110.9923Coordinates: 32°12′37″N 110°59′32″W / 32.2103°N 110.9923°W / 32.2103; -110.9923[1]

Sentinel Peak, more commonly known as "A" Mountain, is a prominent ridge in the Tucson Mountains west of Tucson, Arizona. Tumamoc Hill is immediately west of Sentinel Peak.


Sentinel Peak rises to an elevation of 2,901 feet (884 m) to the west of the Santa Cruz River. The underground ridge of rock, running to the east, once forced groundwater to the surface. The resulting floodplain was used for agricultural fields from about 4,000 years ago until the 1930s. Residents of the nearby village of Schook-schon (Tucson) were visited by Father Eusebio Francisco Kino, who established nearby Mission San Xavier del Bac, in the 1690s. These residents likely used bedrock mortars found on the sides of the peak to grind mesquite beans and corn into flour. When the nearby Presidio of Tucson was constructed in 1775, a sentinel stood on the top of the peak searching the horizon for raiding Apache warriors.

Sentinel Peak is made up of a series of volcanic rocks that represent different types of volcanic activity, though the mountain itself is not a volcano. These layers once extended out west towards the Tucson Mountains and east into the Tucson Basin, where the city is now. Erosion and faulting are responsible for the mountain’s place in Tucson and its conical shape. It rests on a foundation of bedrock, and is dominated by 20- to 30-million-year-old volcanic rocks, made mostly of basaltic andesites, tuff, conglomerates, and scorias. Volcanic ash and breccia, along with ancient lava beds, or lahars, can be also be found on the mountain, as further evidence of a once active volcanic field that formed the Tucson Mountain ranges.

The mountain is more recently known as "A" Mountain because it features a large, painted, man-made basalt rock formation in the shape of the letter "A". Originally built by University of Arizona students, the "A" is maintained by student organizations at the school and has traditionally been painted white. After September 11, 2001, the "A" was painted red, white, and blue, which are the school colors, but primarily was a show of patriotism. The "A" returned to its previous white in 2013. On St. Patrick's Day, the "A" is sometimes painted green.

The idea for the "A" began in 1914 after the Arizona team defeated Pomona College in a big football game. A civil engineering student on the team convinced one of his professors to include the project of creating the "A" atop Sentinel Peak as a class assignment.

On March 4, 1916, the "A" was whitewashed onto the mountain, measuring 70 feet (21 m) wide and 160 feet (49 m) tall. Basalt rock removed from Sentinel Peak was incorporated into foundations and walls throughout historic neighborhoods in Tucson and in the walls surrounding the west side of the University of Arizona campus.

Arizona State University has a more recently created an "A" Mountain (Tempe Butte) near the school's football stadium. During the week of the ASU-UA football game, rival fans and students try to paint the "A" of the opposing school with their own school colors.


See also[edit]


  1. ^ a b "Warner". NGS data sheet. U.S. National Geodetic Survey. Retrieved 2014-02-01.