The Honda SUV left the roadway and smashed into some trees before bursting into flames. Two Calgary teens were killed, and two others are in critical condition. (Washington State Patrol)

Two recent high-school graduates from Calgary were killed in a fiery highway crash in Washington State on the weekend.

Kylie Doxtater and Mikelle Hendrickson, both 18, died when the Honda CR-V they were in left Route 8, southwest of Seattle, at a high speed near milepost 20 on Sunday night and crashed in flames.

"[The vehicle] kept going straight through the corner and went off the roadway, went down an embankment and then struck a group of three to four trees and ... the impact was so great that it pushed the car up the tree about 20 feet," Washington State Trooper Brandy Kessler told CBC News on Tuesday.

Kylie Doxtater, left, and Mikelle Hendrickson seen in a photo posted on Facebook, had graduated from Bowness High School in June.

The coroner's service in Thurston County, Wash., confirmed the women's identities on Monday.

The driver, Benjamin Harms, and a third passenger, Lena Elliott — both also 18 and from Calgary — remain in critical condition in hospital with major burns.

Harms was placed under arrest for vehicular assault and for suspicion of driving under the influence of drugs before being taken to a Seattle hospital, Kessler said.

"We have a drug recognition expert that's a trooper that's specifically trained to determine if somebody's under the influence of drugs," she explained. "They went to the scene and determined that yes, he was under the influence of drugs and that's why he was arrested for vehicular assault."

Charges of vehicular homicide may be pending upon completion of the investigation, Kessler added.

The group was reportedly on its way to Seattle after a road trip to Arizona.

The three women just graduated from Bowness High School. Tribute pages in memory of Doxtater and Hendrickson have been set up on Facebook, where friends and family are sharing stories of the two friends.