The crash happened just after 5 p.m. on State Route 20 and Gibralter Road, just south of Anacortes, said Trooper Mark Francis.
According to State Patrol officials, a 2006 Ford Mustang driven by Ira L. Blackstock, 53, of Oak Harbor was headed south when it crossed the center line and slammed head-on into an Acura Vigor with three teenagers inside.
Both cars were mangled in the wreck.
The 17-year-old driver of the Acura, who family members identified Friday as Nesah Goheen, was critically injured, Francis said. An 18-year-old Oak Harbor woman who was sitting in the passenger seat was also seriously injured. The driver's 17-year-old twin sister, Neah Goheen, who was sitting in the back seat, was killed in the crash.
The survivors were taken to Island Hospital for treatment.
Francis said Blackstock showed signs of impairment. A blood draw will determine if he was intoxicated, and vehicular homicide and vehicular assault charges could be filed.
The twins' friends say this shouldn't be about the driver, and all thoughts should be on the sisters who filled the world with their singing and took park in their high school choir.
"Music wasn't just a hobby for them. They did it at home, they practiced at home," said friend HaileyAdelle Monroe.
Monroe was shocked to learn of the crash and said the entire Oak Harbor community is reeling.
"It's not just the family or their best friends but everyone in this town is going to be incredibly affected by it," she said.
Blackstock appeared in Skagit County District Court early Friday and was ordered held on $70,000 bail.