The incident occurred shortly before 5 a.m. on the southbound 71 before the 60 interchange near Mission Boulevard.
Pomona police said there were no serious injuries as a result of the crash.
One lane was reopened just before 6:30 a.m., but traffic was still backed up for miles. Lanes were expected to remain closed until at least 11 a.m.
Commuters were advised to use alternate routes and avoid the area.