Mother Jones: When I meet Javier Vaca on a dusty strip of blacktop, he’s been walking for three days. The skinny 18-year-old is being carried along in a procession of 7,000 farmworkers and farmers as it crosses California’s Central Valley, his baggy jeans and hoodie standing out amid the work boots and button-downs. He’s been told only one thing that matters: Marching 50 miles might earn him a job. “I don’t want to jack nobody,” Vaca says, as though the thought had crossed his mind. When the …