Interstate 5 is closed in both directions in Siskiyou County following a collision involving at least 60 vehicles.
The California Department of Forestry and Fire Protection, which has crews on the scene, reports that the area affected is between Yreka and Hornbrook.
According to California Highway Patrol traffic incident website, the pile-up began about 6:18 p.m. with semi-trucks crashing on black ice on I-5 near the Collier rest area. Other vehicles were stuck, either because they were stranded on ice or were jammed together. Vehicles couldn't be moved until the state Department of Transportation responded to deal with the icy road conditions.
Cal Fire spokeswoman Julie Hutchinson said a number of people suffered minor to moderate injuries in the series of crashes that stretched for nearly a mile along the northbound side of the freeway.
Hutchinson said she did not know the exact number of people injured, but said the southbound side of the interstate was closed so emergency vehicles could make their way to the scene.
It's not known what caused the pileup, or when the freeway would be open again, but Hutchinson said stretches of the roadway were icy. The National Weather Service has issued a winter weather advisory for the area.