During a routine patrol on Thursday morning, an El Centro Border Patrol agent discovered a tunnel spanning the U.S.-Mexico southern border.

This discovery marks the third cross-border tunnel discovered in the past year, according to U.S. Customs and Border Protection (CBP). The agent made the discovery around 11:30 a.m. after noticing a “depression in the soil along the banks of the All-American Canal.” As the agent approached, the soil gave way, exposing the 18-inch tunnel entrance.

Looking into the three-foot by three-foot-wide tunnel, the agent saw lumber and electrical wiring that indicated it was a cross-border tunnel. The agent secured the scene. The tunnel was found to be 142 feet in length, extending 60 feet south of the international border.

Just three weeks ago, another tunnel was discovered in Calexico.

“This is exactly what our Border Patrol agents are on patrol for,” said El Centro Sector Chief Rodney Scott upon announcement of the find. “They are on the lookout for anything out of the ordinary along our vast Southwest border. This agent saw something that didn’t look quite right and it turned out to be a tunnel.”

“Cross border tunnels pose a significant risk to the safety and security of the United States,” a CBP statement warned. “Anything or anyone could potentially cross into the U.S. via a tunnel.”

A cross-border tunnel discovered last November led into Arizona from Mexico. Breitbart Texas reported that, as of January, the tunnel had not yet been filled.

In March, federal officials announced an inquiry into the discovery of the Calexico cross-border tunnel. A U.S. Immigration and Customs Enforcement (ICE) release stated that it was the 12th large-scale, operational drug smuggling border tunnel discovered since 2006. In that instance the smugglers are believed to have constructed a house around the subterranean drug tunnel exit “for the sole purpose of concealing the exit.”

Follow Michelle Moons on Twitter @MichelleDiana.