An Arlington man is behind bars after admitting he ran over his girlfriend and left her on the side of the road, the sheriff's office said.

The victim was found on Mountain Loop Highway near 119th Street Northeast in Granite Falls.  Police found her boyfriend through a cell phone left at the scene.

Bert Hill was booked into jail Tuesday morning after detectives questioned him at his house. He told them he ran over the victim and drove off.

Witnesses at the scene showed KIRO7 Eyewitness News reporter Lee Stoll how the victim could have easily been hit several more times: Spraypaint around a sharp corner marks the narrow space between the bushes and the highway where the 58-year-old woman was found Monday night.

"Her head was right here on the side of the road," said Cindy Schultz, who was taking her 14-year-old son to get ice cream in Granite Falls. The boy watched as his mother and several other drivers pulled over to help the victim.

"She had a big hole in her arm where it looked like she … I thought she's been shot at first," Schultz said.

Another witness found a cellphone and gave it to Schultz, who handed it to officers.

"By making a few calls on the cellphone, they were able to identify both the victim and the suspect," said  Shari Ireton of the Snohomish County Sheriff's Office.

Officers questioned the victim's boyfriend, 58-year-old Bert Hill.

Investigators said Hill told them the pair was fighting as they drove down the road. Hill said the victim wanted to get out the car so he slowed down and she jumped out.

They said Hill admitted he ran over her and kept going.

Celia Smith heard the sirens from her home nearby.

"It's absolutely horrific," Smith said.

Investigators asked Hill why he spent a night at the couple's home and never called for help.

Officers said he told them he heard the airlift helicopter and figured someone was helping her out.

His girlfriend is at Harborview in serious condition.

Hill was arrested for felony hit-and-run. He'll make his first court appearance on Wednesday.

Bail is set at $10,000.