The wreck, which took place at about 5 p.m. near Mace Boulevard and involved at least four cars, temporarily shut down all eastbound lanes.
Crews worked quickly to remove the vehicles from the road, but the traffic backup stretched all the way to the junction of I-80 and Highway 113.
Officials said 18 people were injured in the wreck. Many ambulances were still at the site as of 6 p.m.
Drivers heading east on I-80 were urged to avoid the area, taking Highway 113 north to Interstate 5 as a detour.