The California Highway Patrol said traffic was being turned around at Hirschdale Road in Nevada County due to the crash near Floriston. All lanes have been blocked.
A photo shared by CHP showed a trailer laying on its side attached to a truck that was dangling off the side of the overpass.
Authorities say there is no estimated time for reopening the roadway.
The cause of the crash was not immediately made available, and it was unclear if there were any injuries.
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