Increased enforcement in San Diego and El Paso has squeezed border crossers into less hospitable corridors, including deserts where hundreds die each year. The Otay Mountains are not the deadliest point along the 2,000-mile border, but they are treacherous.
Dehydration threatens as summer temperatures race past 100 degrees; hypothermia is a danger during winter. Broken wrists and twisted ankles are common, and it's easy to get lost on the lattice of trails. In the last year, 23 migrants have been reported dead in the Border Patrol's San Diego sector, which includes Otay.
Given their outdoor job, the agents must be fit.
Mark Cary, a retired Marine, once took nine hours to trek 7 miles from the dilapidated border fence to the nearest major road, California Route 94. Migrants typically take two days to cover the same route, he says.
All but two of the Air Mobile Unit's 54 agents are men. All but one is under 40 years old -- and he's a supervisor with a desk job.
One recent evening, two agents broke thick sweats as they sped downhill over granite boulders and branches burned during California's 2003 wildfires.
About an hour later, one agent pointed excitedly to the right, stepped off the narrow trail, clutched his rifle, and peered through the dense brush. Within moments, 14 Mexicans were in US custody.
The agents' shift began shortly before sunset at San Diego's Brownfield Municipal Airport, where nearly every night Black Hawk helicopters take agents into mountains where one canyon is known among Mexican migrants as La Espina del Diablo -- the devil's spine -- and trails are named Dead Cow and Tequila Draw.
Just outside Dulzura, a hamlet about 25 miles east of San Diego, Cary and fellow agent Jeff Mielke struck out on one of the countless footpaths blazed by migrants.
Flashlights were kept off to avoid drawing attention. Midway down the canyon, the agents found the 14 migrants -- abandoned by their guide -- resting on rocks near one of the makeshift shrines scattered along the border.
