U.S. Border Patrol agents say they discovered a massive tunnel that spans the U.S.-Mexico border on Wednesday.

The 4,309-foot tunnel starts in Tijuana and ends in the Otay Mesa warehouse district in San Diego, authorities said, according to a USA Today report. Border Patrol told the news outlet that it is the longest tunnel it has ever discovered along the southwest border.

The tunnel is complex, as well, according to the agency. It has an average depth of 70 feet below ground and includes an elevator, an extensive rail cart system, forced air ventilation, high-voltage electrical cables and a drainage system, according to the report.

ADVERTISEMENT

In a statement, Homeland Security Investigations special agent Cardell Morant said, “While subterranean tunnels are not a new occurrence along the California-Mexico border, the sophistication and length of this particular tunnel demonstrates the time-consuming efforts transnational criminal organizations will undertake to facilitate cross-border smuggling."

The tunnel entrance was reportedly found by Mexican authorities in August and then mapped by the San Diego Tunnel Task Force, which is made up of Border Patrol Homeland Security Investigations, the Drug Enforcement Administration and the U.S. Attorney's Office.

The amount of marijuana and meth seized by authorities decreased during fiscal 2019, while the number of heroin seizures increased.

Ralph DeSio, a spokesman for U.S. Customs and Border Protection in San Diego, told the newspaper the decreases in seizures were because the sector's four checkpoints weren't all fully operational in 2019.