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 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.

The incomplete drug smuggling tunnel, which extended more than 1,000 feet inside the U.S., was actively under construction when Border Patrol agents discovered it. SAN DIEGO — U.S. Border Patrol agents found a drug smuggling tunnel linking San Diego and Tijuana in early April, the agency said in a press release on Wednesday.