On May 18, 1980, the north face of Mount St. Helens slid away and triggered a massive eruption that created a lahar that devastated the North Fork Toutle River. The lahar destroyed about of SR 504, including seven of the highway's eight major bridges, leaving only the Kid Valley bridge standing because of its sufficient clearance. The remaining section between Toutle and Kid Valley was buried in up to of sediment, but was able to re-open by September with temporary Bailey bridges and other structures. Several vehicles on the highway were swept away by the lahar, including those carrying some of the eruption's 57 victims.