A new cross-border tunnel used to smuggle drugs from Mexico was found in San Diego, U.S., which is the second such tunnel found within two weeks, authorities said on Tuesday.

According to a spokeswoman for U.S. Immigration and Customs Enforcement, the tunnel was found leading into a California warehouse located in San Diego’s Otay Mesa area, the same area with the previous found one.

The Mexican soldiers were looking for an entry in the south of the border and they traced the origin of the tunnel to a white unnoticed warehouse in Tijuana.

 The previously found tunnel was said to be as long as four football fields, running through two warehouses between Otay Mesa and Tijuana. U.S. authorities seized 17 tons of marijuana on both sides of the border. There were rail systems and sophisticated lighting system in the tunnel.

Meanwhile, on Monday, a Mexican trucker was sentenced to almost 16 years in prison for his involvement in smuggling drugs as he worked in the similar passages discovered last year along the US-Mexico border.

The secret passages have begun turning up since last decade as U.S. authorities heighten enforcement on land. Since October 2008, more than 70 people have been found on the border exceeding the total amount of the previous six years.

The clay-like soil in California provides convenience for the smugglers to dig with shovels.