By ELLIOT SPAGAT
SAN DIEGO (AP) — Authorities have announced the discovery of a major drug smuggling tunnel — running about the length of a six football fields — from Mexico to a warehouse in an industrial area in the U.S. The cross-border tunnel from Tijuana to the San Diego area was built in one of the most fortified stretches of the border, illustrating the limitations of border walls. The tunnel discovered Friday includes electricity, ventilation, railway cars and reinforced walls. It may signal a shift from previous tunnels that were used to smuggle marijuana. Six people from Southern California were charged with conspiracy to distribute cocaine.