A man and woman from Boise, Idaho, were killed Monday when a semitruck slammed into the back of their SUV on Interstate 90 near Hyak on Snoqualmie Pass, triggering a chain-reaction collision, the State Patrol said.

The State Patrol identifies them as 68-year-old Jess Albert Bass and 73-year-old Jean Elaine Bass of Star, Idaho, but their relationship wasn't immediately clear, said State Patrol Lt. Scott Martin. Both were pronounced dead at the scene.

The accident, which occurred in an eastbound lane shortly before 11 a.m. at milepost 56, began when a semitruck stopped for traffic ahead of him, Martin said.

That prompted a car, another semitruck and the SUV, all traveling behind, in that order, to stop or come to a near stop, Martin said.

A third semitruck didn't stop and rear-ended the SUV, Martin said.

The SUV was pushed into the semitruck ahead of it, Martin said. That semitruck pushed the car ahead of it into the semitruck that had initially stopped, Martin said.

Martin said the cause of the crash appeared to be inattention on the part of the semitruck driver who didn't stop.

Weather conditions were clear, with bare and dry road along a new section of the freeway, he said.

Several people in the other vehicles were transported by ambulance with nonlife-threatening injuries, Martin said.

A dog in the SUV jumped from the vehicle and will be taken to the family of the victims by the state Department of Transportation, he said.

Eastbound traffic was reduced to one lane. Monday afternoon, there was a backup of seven miles, the Transportation Department said. Westbound traffic remained at two lanes.

Steve Miletich: 206-464-3302 or smiletich@seattletimes.com