Sentinel Peak (Arizona) Facts for Kids

Quick facts for kids Sentinel Peak
"A" Mountain
The "A" on Sentinel Peak
Highest point
Elevation	2,901 ft (884 m) NAVD 88
Prominence	267 ft (81 m)
Geography
Sentinel Peak Location in Arizona
Location	City of Tucson Pima County, Arizona, U.S.
Parent range	Tucson Mountains
Topo map	USGS Tucson

Sentinel Peak is a mountain in Tucson, Arizona. It stands about 2,897 feet (883 meters) tall. This peak is part of the Tucson Mountains, located southwest of downtown Tucson. Many people also know it as "A" Mountain.

Long ago, the first people to live in the valley grew crops near the base of this mountain. The name "Tucson" actually comes from the O'odham words Cuk Ṣon. These words mean "at the base of the black hill," which describes Sentinel Peak.

In the 1910s, students from the University of Arizona built a huge letter "A" on the mountain. They used local rocks for this project. The "A" is 160 feet (49 meters) tall and can be seen from far away. Today, Sentinel Peak is part of a large park. This park covers 272 acres (110 hectares) and is the biggest natural park in Tucson.

A Look at Sentinel Peak's Past
- Ancient Tools and Visitors
- Guards on the Peak
How Sentinel Peak Was Formed
- Remains of Ancient Lava Flows
- Layers of Rock
Why It's Called Sentinel Peak
- The Sentinel Station
- What Was Left Behind
The Famous "A" on the Mountain
Images for kids
See also

A Look at Sentinel Peak's Past

The land at the bottom of Sentinel Peak was very good for farming. People used it for growing crops for a very long time, from about 4,000 years ago until the 1930s.

Ancient Tools and Visitors

On the sides of the peak, people have found bedrock mortars. These are special holes in rocks. It is believed that ancient people used them to grind corn and mesquite beans into flour.

In the 1690s, a priest named Father Eusebio Francisco Kino visited the O'odham people living here. He later started the nearby Mission San Xavier del Bac.

Guards on the Peak

Later, in 1775, a fort called Presidio San Augustin del Tucson was built. Guards, called sentinels, were placed on Sentinel Peak. Their job was to watch for Apaches who might be raiding the area. This is how the mountain got its name.

How Sentinel Peak Was Formed

Sentinel Peak is made of different layers of igneous rock. These rocks were formed by hot, melted rock that cooled and hardened. This shows that there was a lot of volcanic activity in the past. However, the mountain itself is not a volcano.

Remains of Ancient Lava Flows

Sentinel Peak is one of several hills at the eastern edge of the Tucson Mountains. These hills are mostly what is left of old lava flows. These lava flows happened about 20 to 30 million years ago. They once spread west towards the Tucson Mountains and east into the area where Tucson city is now. Over time, wind and water wore away the rock. This process, called erosion, along with cracks in the earth (faulting), gave the peak its cone shape.

Layers of Rock

The very top of the hill has a type of rock called basaltic andesite. This rock is about 23 to 24 million years old. Below it is a thick layer of tuff, which is compacted volcanic ash. This layer is 30 to 36 meters thick. Underneath that is another layer of basaltic andesite. Both of these layers are 26 to 28 million years old. At the very bottom of the hill, on the south side, there are even older rocks. These tuffs and andesite rocks are about 60 million years old.

You can also find volcanic ash and breccia (rock made of broken pieces of minerals) on the mountain. There are also ancient lava beds, called lahars. All of these show that the Tucson Mountain range was once a very active volcanic area.

Why It's Called Sentinel Peak

Historian David Leighton explained the name "Sentinel Peak" in a newspaper article in 2016.

The Sentinel Station

He wrote that in the early days of Tucson, Native Americans built a small fort on top of this mountain. This fort became known as the sentinel station. A sentinel, or guard, was always posted there. Their job was to watch for enemies coming closer, especially Apache Indians.

During the U.S. Civil War, soldiers were also stationed at this lookout point. They even stretched a canvas over the stone fort to protect themselves from the sun.

What Was Left Behind

By 1883, only parts of the fort remained. There was a round wall, about 3 feet thick, made of large rocks. It enclosed an area about 8 feet across. To the north, there was a smaller wall, about two feet high and 10 feet long. There were also signs of another small round wall to the east.

In 1925, some parts of the fort were still there. By then, the mountain was already being called "A" Mountain. Mr. Leighton said that the name Sentinel Peak comes directly from the sentinel station and the guards who worked there.

The Famous "A" on the Mountain

After a big football game in 1914, a student from the University of Arizona had an idea. His team, the Arizona football team, had just won against Pomona College. He convinced his engineering professor to make a class project out of designing a huge letter "A" on Sentinel Peak.

Building the "A"

Students worked hard to complete the project. On March 4, 1916, the giant "A" was finished. It was 70 feet (21 meters) wide and 160 feet (48 meters) tall. They painted it white on the east side of the peak. The rocks used to build the "A" came from a quarry at the base of the mountain. This quarry also provided stone for many buildings and walls around Tucson, including the wall around the University of Arizona campus.

Changing Colors of the "A"

The "A" is usually painted white. But sometimes, its color changes for special reasons:

In 2003, it was painted black to protest the Iraq War.
Two weeks later, the Tucson City Council decided to paint it red, white, and blue to honor American troops.
Ten years later, the council decided to paint it white again.
For St. Patrick's Day, the "A" has sometimes been painted green.
On May 8, 2020, it was painted blue to thank healthcare workers during the COVID-19 pandemic.

Rivalry with ASU

Arizona State University also has an "A" Mountain near their football stadium. During the week of the Territorial Cup game between Arizona and ASU, rival fans sometimes try to paint the "A" of the other school with their own team colors.

Images for kids

Dense stands of saguaros at the base of Sentinel Peak
Sentinel Peak, standing behind a wrecked bridge along the Santa Cruz River during the flood of 1915
"A" Mountain (right) and Tumamoc Hill (left) in the distance, looking west across the Tucson Valley
Tucson as seen from Sentinel Peak