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Saguaro National Park

geography Maturity 7-9 Next article →

Saguaro National Park is a protected area in southeastern Arizona, USA. It preserves the unique landscapes of the Sonoran Desert. The park is unique because it consists of two separate areas. The Tucson Mountain District (TMD) lies west of Tucson. The Rincon Mountain District (RMD) lies east of Tucson.

TMD trail map
TMD trail map

Both districts protect important plants and animals. The park is named after the giant saguaro cactus, or *Carnegiea gigantea*. This cactus is native to the Sonoran Desert. It does not grow naturally anywhere else.

A large cactus (Carnegiea gigantea) at Saguaro National Park
A large cactus (Carnegiea gigantea) at Saguaro National Park

The two districts have very different geological histories. The surface rocks in the TMD differ greatly from those in the RMD. About 30 million years ago, the Earth's crust began to stretch. This crustal stretching displaced rocks from beneath the Tucson Mountains. These rocks moved to form the Rincon Mountains. The RMD is much higher and wetter than the TMD. The Rincons are part of the Madrean Sky Islands. These are mountain ranges located between the southern Rocky Mountains and the Sierra Madre Oriental in Mexico. Because of this, the RMD has high biodiversity. It supports many plants and animals that do not live in the TMD.

Saguaro cactus forest
Saguaro cactus forest

The geology of the park is incredibly ancient. The oldest rocks are called Pinal Schist. This schist predates the Basin and Range Province by 1.7 billion years. In the RMD, you can find 1.4-billion-year-old altered granites. About 600 million years ago, shallow seas covered this region. This led to the creation of sedimentary rocks like limestone, sandstone, and shale. In the late 19th century, people mined limestone here to make mortar. Several old lime kilns still exist in the RMD today.

Javelina Rocks in the RMD
Javelina Rocks in the RMD

Volcanic activity also shaped the landscape. About 70 million years ago, explosive eruptions formed the Tucson Mountains. The roof of a central volcano eventually collapsed. This created a large structure called a caldera. Debris flows and lava flows filled this caldera over time. The TMD contains volcanic rocks from these events. You can see a granitic remnant of the magma chamber at the Sus Picnic Area. This granite cooled and crystallized far below the surface. In the RMD, the most common rock is Catalina gneiss. This is a type of banded, crystallized granite.

Javelina Rocks in the RMD
Javelina Rocks in the RMD

Many people have lived on these lands throughout history. The Hohokam lived in villages here from AD 200 to 1450. They left behind pottery and petroglyphs, which are carvings in rock.

Sunshine-AZ Photo Saguaro Park West Petroglyphs
Sunshine-AZ Photo Saguaro Park West Petroglyphs

Later, Spanish explorers and missionaries arrived in the region. In the late 1800s, miners and ranchers moved into the area. The Copper King Mine produced many tons of copper, gold, and lead. It closed in 1942 when it was no longer profitable. Ranchers also grazed thousands of cattle on the land. Some families even built homesteads, like the Freeman Homestead in the RMD.

Saguaro National Park1935
Saguaro National Park1935

The park's status has changed through several presidential actions. In 1933, President Herbert Hoover established the Saguaro National Monument. This original monument was only in the Rincon Mountains. In 1961, President John F. Kennedy added the Tucson Mountain District. He renamed the original area the Rincon Mountain District. Finally, the United States Congress combined both districts into a national park in 1994. In 2016, the total area of the park was about 222,000 acres. The RMD is much larger than the TMD. About 70 percent of the entire park is designated wilderness.

Rincon Mountain District map
Rincon Mountain District map

Today, visitors enjoy many activities in the two districts. People go hiking on many different trails. Others enjoy sightseeing along paved roads near the visitor centers. Bicycling and horseback riding are allowed on selected roads and trails. The RMD offers limited wilderness camping. However, there is no overnight camping allowed in the TMD. The climate is classified as a hot semi-arid climate. The weather can be intense, with summer rains causing lightning and flash floods.

Fairy duster Saguaro NP
Fairy duster Saguaro NP
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🖼️ Images & Media (9)
File:A large cactus (Carnegiea gigantea) at Saguaro National Park.jpg
A large cactus (Carnegiea gigantea) at...
File:Javelina Rocks in the RMD.jpg
Javelina Rocks in the RMD.jpg
File:Sunshine-AZ Photo Saguaro Park West Petroglyphs.jpg
Sunshine-AZ Photo Saguaro Park West...
File:Saguaro National Park1935.jpg
Saguaro National Park1935.jpg
File:Fairy duster Saguaro NP.jpg
Fairy duster Saguaro NP.jpg
File:Saguaro cactus forest.jpg
Saguaro cactus forest.jpg
File:Javelina in Saguaro National Park.jpg
Javelina in Saguaro National Park.jpg
File:TMD trail map.png
TMD trail map.png
File:Rincon Mountain District map.png
Rincon Mountain District map.png
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