ICE says Homeland Security Investigations agents, working with Mexican authorities, found the 183-foot-long tunnel at a home Aug. 2 in Mexicali near the border.
"The tunnel, which has an entrance measuring 12 feet by 10 feet, extends 3 feet north of the international border wall, but has no exit on the U.S. side of the border," ICE said in a news release that featured images of the tunnel.
The agency says the tunnel was equipped with electricity, ventilation and even a rail system with a cart and an electric hoist.
The investigation is ongoing and is being led by HSI with help from the El Centro Sector Border Patrol and the government of Mexico.