The Washington State Patrol is hoping someone will step forward as a witness to a serious, head-on collision that occurred just after 1 a.m. Thursday.

The crash was on state Route 169 near 383rd Street north of Enumclaw and blocked traffic in both directions as authorities conducted an investigation.

According to a State Patrol press release, a white Chevrolet Tahoe driven by Seattle resident Christine Bass was traveling north on SR 169 when it crossed over the centerline. The Tahoe collided head-on with a white Chevrolet Malibu traveling southbound. The Malibu driver, Black Diamond resident Vicki Harp, was airlifted to Harborview Medical Center with serious injuries.

Bass was placed under arrest for investigation of vehicular assault and transported by ambulance to Harborview with serious injuries. The WSP said alcohol is believed to be a factor in the collision.

Detectives are seeking witnesses who observed the collision or either of the involved vehicles prior to the collision. Witnesses should contact Det. Russ Haake at 425) 401-7717.