None of the Canadians involved in the 23-vehicle pile-up were hurt.
The accident closed both northbound and southbound lanes of the highway for most of the day near Mt. Vernon at Anderson Road.
Images from the scene show cars bent and twisted and a larger multi-wheeled vehicle turned on its side.
Officials say a dump truck full of gravel heading south crossed into the northbound lane after the driver suffered a medical incident.
The dump truck collided with other vehicles, which were travelling slowly due to another incident in the area.
It took into the evening Saturday for crews to remove the wreckage and gravel that spilled.
All lanes of the I-5 finally re-opened on Saturday night after 7 p.m. PT.