ROCKY MOUNTAIN NATIONAL PARK – Park ranger Jeff Christensen died of head injuries from a fall on the same day he left to patrol the rugged backcountry of Rocky Mountain National Park, park officials said Monday.Christensen’s body was found after an intensive, eight-day search over 26 square miles of mountainous wilderness. He was believed to have died between 6 p.m. and midnight on July 29 – the same day he left on a patrol, according to an autopsy report done by the Larimer County Coroner’s Office and released by the park.Park officials said they were still investigating the circumstances of Christensen’s death, said Al Nash, spokesman for the National Park Service headquarters in Washington. Christensen was believed to be the first ranger to die on duty in the park’s 90-year history.A hiker found the 31-year-old’s body near Spectacle Lakes at about 13,000 feet Saturday, three miles east of where he had begun his patrol. The site was two to three miles away from an area where searchers heard gunshots and radio static that they thought might have been Christensen trying to signal them in the middle of last week.Dale and Chris Christensen of Forest Lake, Minn., arrived in Colorado since Tuesday to wait for word on their son. They thanked scores of volunteers who looked for the younger Christensen.Dale, a machinist, and Chris, an administrator for an insurance firm, said their son knew he wanted to move to Colorado while he was still attending the University of Minnesota-Duluth.An avid skier, Christensen worked on the Winter Park ski patrol and was hired as a seasonal ranger at Rocky Mountain National Park in 2002. Park officials said this was Christensen’s first summer on the park’s east side, and it may have been his first time patrolling the area where he died.