Prisoners participating in the Wild Horse Inmate Program train mustangs that will eventually be adopted by the U.S. Border Patrol, providing the agency with inexpensive but agile horses. The inmates on their turn will be equipped with skills and insights they hope to one day carry with them from Florence State Prison.

The horses are trained in Florence, Arizona and applied in border cities like Jacumba and also San Diego in California. They are critical for patrolling the rugged and remote stretches of the Mexican border to detect illegal crossings by migrants and drug trafficking. Just 654 miles (1053 kilometers) of fence exist between the United States and Mexico, accounting for about a third of the border.

The rest is defined by mountains, rivers, private ranches and wild country - terrain more suited for horses, which all agents had back when Border Patrol was founded in 1924. Here, Border Patrol agents head out on patrol along the fence near Jacumba, California.

On horseback, the agents can navigate desolate stretches of land that vehicles cannot. The mustangs are sure-footed on steep terrain, crossing creekbeds without hesitation and stepping spryly over rattlesnakes. Some 55,000 mustangs roam the Western United States. Here, wild horses are herded into corrals in Milford, Utah.

At the prison in Florence, a cactus-dotted town about 140 miles north (225 km) of the Mexican border, most inmates don't have experience with horses. Over the course of four to six months, the men train their horses to tolerate bridles and saddles, respond to commands to trot and canter and perform footwork that will come in handy on the uneven desert terrain along the border.

The task of the Florence inmates who train the horses is, at times, thick with irony: Some are Mexican nationals, apprehended on the border for drug-related offenses. The inmates, though, say they don't mind that the horses help law enforcement. They are simply happy the animals no longer face thirst and starvation in the drought-stricken West.

The San Diego border patrol unit has 28 horses, of which many were adopted from the Florence prison. These adoptions are key to the government's effort to stem the growing population of mustangs. A federal law tasked the Bureau of Land Management with managing wild horse and burro populations, both to protect the animals and to ensure that vegetation was not overgrazed and water sources depleted.

Florence began its horse training program in 2012, and while it is too early to assess the long-term effects on participating inmates, of the 50 or so who have gone through it and have been released, none has returned to prison.

"It really feels like the Wild West out where we patrol for sure," says Bobby Stine, supervisory agent of the San Diego Sector Horse Patrol Unit. "There's just not a lot of law enforcement presence, except for us."