Arizona’s Sonoran Desert: Organ Pipe Cactus National Monument and Saguaro National Park

The park’s namesake cactuses, the organ pipes, stand up to 25 feet tall.

Cactuses frame cactuses in the Sonoran Desert.

A dying cholla -- also known as jumping cactus -- with organ pipe cactuses in the background.

The outer waxy layer of a dead cactus looks like alligator skin.

A view of the desert inside Organ Pipe Cactus National Monument.

Little metal sculptures of desert animals line the windows at the Organ Pipe Cactus Monument Visitor Center near Ajo, Ariz.

A stone hat and plaque memorialize Park Ranger Kris Eggle, who was killed while chasing drug smugglers in 2002. Eggle’s death earned the park a reputation as one of the most dangerous national parks in the country.

A sign warns visitors about possible dangers inside the park. After Eggle’s death, the park ramped up enforcement, and now the park seems to be a safe place to observe the cactus and wildlife.

U.S. Customs and Border Protection vehicles man the metal border fence with trucks, cameras and regular patrols in the park.

Humanitarian groups have placed blue tanks of water to aid immigrants crossing the desert in Organ Pipe National Monument.

San Diego residents Frank Yancey and Barbara Deese stand with their dog Sophie at a campground in the park.

“This park is gorgeous and has some of the best facilities around,” said Frank Yancey, a retired school teacher. “When we first came a lot of the roads were closed, but we have never had any problems.”

On the outskirts of Tucson, Saguaro National Park comes to life shortly after sunrise with the park’s namesake cactuses reaching for the skies.

A grove of saguaro cactuses. The Sonoran Desert is one of the hottest and driest regions on the continent, yet plants and animals are able to survive through special adaptations.

A visitor snaps a picture of a young saguaro cactus. The young succulents live for years under a tree or bush, protected from the heat and sun until they reach maturity.

Visitors snap pictures of the iconic cactuses along Cactus Forest Drive in Saguaro National Park.

A closeup of a cactus along Cactus Forest Drive.

Ranger Jeff Wallner leads a nature talk with a group of visitors off Cactus Forest Drive in Saguaro National Park.

A bicyclist zooms past lush desert plants and cactuses on Cactus Forest Drive in Saguaro.

After a short hike (.3 mile) and a scramble over some rocks, the Signal Hill Trail leads to ancient petroglyphs datng back more than 800 years in Saguaro National Park near Tucson.

An ocotillo reaches for the sun on Cactus Forest Drive.

Visitors walk down the newly improved Mica View Trail in Saguaro.

Park ranger Cam Juarez on Mica View Trail.

A butterfly lands on a flower along the Mica View trail.

After a short hike (.3 miles) and a scramble over some rocks, the Signal Hill Trail leads to ancient petroglyphs dating back more than 800 years.

Petroglyphs off Signal Hill Trail.

A butterfly lands on a prickly pear cactus.

Homes in Tucson can be seen near the border of Saguaro National Park.