The desolate fist of Otay Mesa extends for 8 miles along the U.S.-Mexico border, from the rugged San Ysidro Mountains on the east to the edge of Interstate 5 on the west. Few people live here. Except for some tomato farms, several squatter’s homes, and the airport at Brown’s Field, the mesa is a no-mans land of wild mustard fields and scrub brush broken only by a few eucalyptus trees and thousands of miles of deeply rutted trails. What keeps this barren strip separate from the tennis courts and golf courses of prosperous San Diego County is not geography or even a commitment to open space. Policing undocumented immigrants, not recreation or conservation or real estate, dominates the mesa strip, creating a zone that seems something like out of Joseph Conrad’s Heart of Darkness: a territory in constant state of low-key conflict, where there are no apparent front or rear lines, no visible heroes or enemies, no sources of information that are not suspect. Entry to this area demands submission.