The thieves come in the dead of night, after it rains and the hillsides are empty, or during a full moon. They disappear into jungly thickets on steep, remote hillsides, stepping carefully through the groves to avoid crunching leaves before doing their dirty work. They operate stealthily, without clippers, amassing warty, thick-skinned booty by the hundreds. Allen Luce, a retired beekeeper, suspected the worst recently when he spied an unfamiliar red pickup truck parked beside the lush canopies of his neighbors' thousand-acre avocado grove. "At a dollar or more a pound, it adds up pretty fast," he said, speaking of the Hope diamond of these parts: the avocado. They call it green gold. "When the Super Bowl comes, there is going to be thievery," Mr. Luce said. "People want guacamole."