The multi-vehicle crash happened just before 3 p.m. on the eastbound 210 near the Huntington Drive exit.
It's unclear what exactly led to the collision, but afterward debris was scattered all over the roadway and a truck was smashed into the side of a smaller vehicle with a Girl Scouts logo painted on the side.
Traffic was blocked on the eastbound side of the 210, with cars backing up for at least four miles. Authorities were letting one lane of traffic exit near the crash scene. Cars on the westbound side were passing by the scene slowly.
The cause of the crash remains under investigation. The freeway was fully reopen about five hours after the crash.