Sentinel Peak (Arizona)
Encyclopedia
Sentinel Peak, more commonly known as "A" Mountain, is a prominent ridge
in the Tucson Mountains
Tucson Mountains
The Tucson Mountains are a minor mountain range west of Tucson, Arizona. The Tucson Mountains, including Wasson Peak, are one of four notable mountain ranges surrounding the Tucson valley...

 west of Tucson, Arizona
Arizona
Arizona ; is a state located in the southwestern region of the United States. It is also part of the western United States and the mountain west. The capital and largest city is Phoenix...

.

Sentinel Peak rises 2,897 feet into the air 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
Mission San Xavier del Bac
Mission San Xavier del Bac is a historic Spanish Catholic mission located about 10 miles south of downtown Tucson, Arizona, on the Tohono O'odham San Xavier Indian Reservation...

, 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
Apache
Apache is the collective term for several culturally related groups of Native Americans in the United States originally from the Southwest United States. These indigenous peoples of North America speak a Southern Athabaskan language, which is related linguistically to the languages of Athabaskan...

 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 andesite
Basaltic andesite
Basaltic andesite is a black volcanic rock containing about 55% silica. Minerals in basaltic andesite include olivine, augite and plagioclase. Basaltic andesite can be found in volcanoes around the world, including in Central America and the Andes of South America. Basaltic andesite is common in...

s, 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
Basalt
Basalt is a common extrusive volcanic rock. It is usually grey to black and fine-grained due to rapid cooling of lava at the surface of a planet. It may be porphyritic containing larger crystals in a fine matrix, or vesicular, or frothy scoria. Unweathered basalt is black or grey...

 rock formation in the shape of the letter "A". Originally built by University of Arizona
University of Arizona
The University of Arizona is a land-grant and space-grant public institution of higher education and research located in Tucson, Arizona, United States. The University of Arizona was the first university in the state of Arizona, founded in 1885...

 students, the "A" is maintained by student organizations at the school and has traditionally been painted white. After September 11, 2001
September 11, 2001 attacks
The September 11 attacks The September 11 attacks The September 11 attacks (also referred to as September 11, September 11th or 9/119/11 is pronounced "nine eleven". The slash is not part of the pronunciation...

, the "A" was painted red, white, and blue, which are the school colors, but primarily was a show of patriotism
Patriotism
Patriotism is a devotion to one's country, excluding differences caused by the dependencies of the term's meaning upon context, geography and philosophy...

. Since then, the "A" has not returned to its previous white. On St. Patrick's Day, the "A" is sometimes painted green
Green
Green is a color, the perception of which is evoked by light having a spectrum dominated by energy with a wavelength of roughly 520–570 nanometres. In the subtractive color system, it is not a primary color, but is created out of a mixture of yellow and blue, or yellow and cyan; it is considered...

.

The idea for the "A" began in 1914 after the Arizona team defeated Pomona College
Pomona College
Pomona College is a private, residential, liberal arts college in Claremont, California. Founded in 1887 in Pomona, California by a group of Congregationalists, the college moved to Claremont in 1889 to the site of a hotel, retaining its name. The school enrolls 1,548 students.The founding member...

 in a big football
American football
American football is a sport played between two teams of eleven with the objective of scoring points by advancing the ball into the opposing team's end zone. Known in the United States simply as football, it may also be referred to informally as gridiron football. The ball can be advanced by...

 game. A civil engineering
Civil engineering
Civil engineering is a professional engineering discipline that deals with the design, construction, and maintenance of the physical and naturally built environment, including works like roads, bridges, canals, dams, and buildings...

 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
Mountain
Image:Himalaya_annotated.jpg|thumb|right|The Himalayan mountain range with Mount Everestrect 58 14 160 49 Chomo Lonzorect 200 28 335 52 Makalurect 378 24 566 45 Mount Everestrect 188 581 920 656 Tibetan Plateaurect 250 406 340 427 Rong River...

, measuring 70 feet wide and 160 feet tall. Basalt
Basalt
Basalt is a common extrusive volcanic rock. It is usually grey to black and fine-grained due to rapid cooling of lava at the surface of a planet. It may be porphyritic containing larger crystals in a fine matrix, or vesicular, or frothy scoria. Unweathered basalt is black or grey...

 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
University of Arizona
The University of Arizona is a land-grant and space-grant public institution of higher education and research located in Tucson, Arizona, United States. The University of Arizona was the first university in the state of Arizona, founded in 1885...

 campus.

Arizona State University
Arizona State University
Arizona State University is a public research university located in the Phoenix Metropolitan Area of the State of Arizona...

 has a more recently-created "A" Mountain (Tempe Butte
Tempe Butte
Tempe Butte is the official name of an andesite butte of volcanic origin, located partially on Arizona State University's Tempe campus in Tempe, Arizona. It is often referred to by locals as A Mountain, after the gold-painted letter 'A' near the top...

) near the school's football stadium. During the week of the ASU-UA football
American football
American football is a sport played between two teams of eleven with the objective of scoring points by advancing the ball into the opposing team's end zone. Known in the United States simply as football, it may also be referred to informally as gridiron football. The ball can be advanced by...

game, rival fans and students try to paint the "A" of the opposing school with their own school colors.
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