A cross border tunnel was discovered near Calexico Friday, marking the second such discovery in three weeks, according to a news release from U.S. Customs and Border Protection.

An El Centro Sector Border Patrol agent first found the hidden tunnel around 11:30 a.m. while conducting routine patrol duties along the border, the release stated.

The agent noticing a depression in the soil along the banks of the All-American Canal and approached it. As the agent did so, the soil gave way, exposing an 18-inch hole with lumber and electrical wiring inside, according to the release.

The tunnel — approximately three feet wide and 142 feet in length — was quickly secured, authorities said. It began about 60 feet south of the border in Mexico.

“This is exactly what our Border Patrol agents are on patrol for,” El Centro Sector Chief Rodney Scott said in the release. “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.”

The discovery marks the third time a cross border tunnel was found in the Calexico area within a year, according to U.S. Customs and Border Protection.

Three weeks ago, four people were arrested after Border Patrol agents located an alleged secret drug tunnel underneath a three-bedroom house in Calexico, authorities said. The tunnel’s entrance was inside a restaurant in Mexicali, Mexico.

More than 1,500 pounds of marijuana worth approximately $6 million was confiscated in the March 23 incident.

CNN contributed to this story.