Mexican officials found a cross-border tunnel that started in a home in Jacume, Mexico, less than 100 yards away from the U.S. border.

After mapping the 31-feet deep and 627-feet long tunnel, U.S. officials determined that the tunnel reached 336 feet into the area in Jacumba, Calif., the Los Angeles Times reported.

U.S. Border Patrol, Homeland Security Investigations, and Drug Enforcement Administration officials determined that even though the tunnel does cross the U.S.-Mexican border, it does not have an exit yet into the U.S.

The beginnings of an exit shaft reached 15 feet but had not broken the surface.

“Sophisticated tunnels take a lot of time and money to make,” said Border Patrol Agent Tekae Michael. “When we find them, they’re a pretty big deal.”

Michael said that these types of tunnels are not uncommon in the area, and the tunnel was likely made to transport drugs into the U.S. from Mexico.

Border Patrol Agent Vincent Pirro said that once investigations into such tunnels are completed, agents usually fill them in.

In the tunnel agents found a rail system, a solar panel system that powered lighting and ventilation, as well as a system to pump out water.

The entrance to the tunnel was found by Mexican police during a mid-September operation, and after discovering the tunnel they worked with U.S. agencies to explore it further.

There have been no arrests made by U.S. officials so far as the tunnel remains under investigation, Michael told the L.A. Times.