Los Angeles ? Three tons of marijuana worth an estimated $20 million on the street was found in a rental truck abandoned on a California freeway onramp this week, authorities said Friday.

A California Highway Patrol officer discovered the stash when he stopped to check on a truck in Ontario, a Los Angeles suburb, about 9 p.m. Wednesday, said highway patrol spokesman Sgt. Telfinues Preszler Jr.

No one was around, and nothing appeared to be wrong with the vehicle, he said. The truck was unlocked and its engine still warm. The officer called for a tow truck and discovered the marijuana when he opened the back to inventory its contents.