BIG BEND, TEXAS—Drug smugglers are using their routes along the Texas-Mexico border to traffic in pre-Colombian artifacts looted from the Rio Grande’s limestone canyons, according to Tim Stone of Homeland Security Investigations. Agents have recovered pottery, stone points, figurines, and 2,000-year-old shoes, all estimated to be worth $250,000 on the black market. “Like almost any crime, it’s really the same—it’s profit,” he said.