MAP: Tohono O'odham Nation; CREDIT: Los Angeles Times; IN CUSTODY: Immigrants found on the Tohono O'odham Nation are taken to a Border Patrol station, their backpacks left stacked outside. This year, 27,130 people have been arrested in the area.; PHOTOGRAPHER: Don Bartletti Los Angeles Times; IN DANGER: Mexicans rest in the desert south of Tucson. Last year, 69 people died crossing Indian land.; PHOTOGRAPHER: Don Bartletti Los Angeles Times; EYES PEELED: [Oliver Smith], an Indian who patrols his neighborhood three times a day, stops his pickup at the San Miguel Gate, which separates Mexico from the U.S. There are no authorities on either side. "The Mexicans come because it's open," Smith says.; PHOTOGRAPHER: Don Bartletti Los Angeles Times; PACKED IN: Mexicans crowd the back of a truck in Sasabe, Mexico, the staging point for those heading through the reservation. Up a dirt road, everyone will jump out and run for the border.; PHOTOGRAPHER: Don Bartletti Los Angeles Times; ON EDGE: A U.S. Park Ranger patrols the Mexican border in Arizona. With more than 1,500 immigrants crossing the Tohono O'odham Nation every day, high-speed chases are frequent.; PHOTOGRAPHER: Don Bartletti Los Angeles Times