The California Highway Patrol says the big rig was carrying 15-foot metal poles when it lost its load, spreading across all lanes.
Officers say the far two right lanes, starting south of Grapevine Road, were closed as crews worked to clean up the debris.
Caltrans cameras near the scene of the crash showed traffic at a near standstill for several hours.
All lanes have since been cleared and have reopened to traffic.
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Caltrans says traffic was backed up 30 miles.
This comes one day before Thanksgiving, traditionally one of the busiest travel days of the year.