The collision was reported shortly after 11 a.m. on the interstate, just south of Grapevine Road, according to the California Highway Patrol.
The CHP said the semitruck was carrying 15-foot metal poles when it lost its payload, spreading the poles across all lanes.
Crews were actively working to clean up the debris.
CalTrans said traffic was backed up for 20 miles at one point. Caltrans cameras near the crash site showed traffic at a near-standstill.
All lanes have since been cleared and reopened to traffic right before 7 p.m., but there was still a long backup.
The traffic nightmare came one day before Thanksgiving, traditionally one of the busiest travel days of the year.
The Associated Press contributed to this report.