Fullenkamp attempted to avoid the big rig by driving onto the northbound shoulder, but the two vehicles still collided. The semi caught fire and became fully involved in flames after the crash, but Nakai escaped with non-life threatening injuries.
Fullenkamp was dead at the scene.
WHP troopers were still trying Wednesday to determine why Nakai, who was taken to Memorial Hospital in Craig, drifted into Fullenkamp's lane, Townsend said.
It took four hours for troopers to clear the scene of the accident.
In a statement Wednesday, Utah DWR Director Gregory Sheehan said that Fullenkamp's death was met with "profound sadness"by friends and colleagues.
Fullenkamp leaves behind a wife, Tanna, a Forestry, Fire and State Lands employee, and their 1-year-old son, Jake.
"Today will be counted among the darkest of our careers, but we must move forward in a way that honors Keith's memory and his service to the people of Utah," Sheehan said. "For those of you who knew Keith, you know that he was a great friend to all.
"For now, our focus and priority must be in ensuring the Fullenkamp family receive the care, support, and resources to get them through the coming days and weeks," he added. "Life is fragile, precious and unpredictable. Go home to your families and hold them close."
As a DWR sergeant, Fullenkamp supervised several conservation officers in the agency's northern Utah region. He also was instrumental in organizing several community and youth events, including a waterfowl fair Sept. 7 at Farmington Bay.