At around 8:20 p.m., a fuel delivery tanker reportedly struck a large metal object in the right southbound lane of Highway 101 near Magnolia Drive, CHP Officer Peter Van Eckhardt said.
The object, which weighed as much as 200 pounds, apparently punctured the fuel tank of the big rig and not its cargo container, Van Eckhardt said.
No one was injured in the collision, but an unknown amount of diesel fuel spilled across approximately 150 feet of both southbound lanes.
A Caltrans hazardous materials team responded with an absorbent to clean up the spill, requiring the closure of one or both lanes for more than three hours.
The CHP could not confirm whether the spill had reached any waterways via highway storm drains, but estimated less than a gallon is likely to have done so before cleanup crews responded and prevented further seepage.
A Sig-alert issued at 8:45 p.m. was cancelled when the highway was cleared at 11:40 p.m.