U.S. Border Patrol agents have uncovered a sophisticated underground tunnel stretching more than 1,000 feet into the United States from Mexico as part of a drug-smuggling operation in Southern California.

The US Customs and Border Patrol a large-scale US-Mexico drug smuggling tunnel. A border patrol chief warned that the tunnel is proof that terrorists are going underground.

The 3,000-foot tunnel — which reached depths of around 50 feet underground at its deepest point — was equipped with lighting, electrical wiring, ventilation systems and a track system.