Their account, and a runner’s November clash, preceded a New Year’s Day discovery on the Crosier Mountain trail.
GLEN HAVEN, CO — A Northern Colorado couple says three mountain lions surrounded them on the Crosier Mountain trail after Thanksgiving, weeks before a woman was found dead there on Jan. 2 with injuries consistent with a mountain lion attack. Wildlife officers have since euthanized two lions near the scene and shut the trail area.
The reported close calls underscore how a remote, popular foothills route in unincorporated Larimer County became the focus of a rare fatal encounter. Colorado Parks and Wildlife says mountain lion attacks on people are uncommon, and the medical examiner is still determining the woman’s cause and manner of death. But the agency’s investigators say the scene matched signs of a lion attack, prompting an intensive search by ground teams and aircraft for the cats that frequented the area. The response has raised new questions about recent sightings, warning signs posted, and how officials tracked reports before the holiday week.
Andrew Dieffenbach of Greeley said he and his partner, Lindsey Jones, were nearing the summit above Glen Haven when they noticed a lion crouched below an aspen, locking eyes. “We definitely felt we were being hunted,” Dieffenbach said in an interview. The couple yelled and threw rocks. As they edged downhill to create distance, a second lion dropped from a ledge and “started jaunting toward us in an aggressive manner,” he said, showing teeth and moving sideways through brush. Then, Dieffenbach caught a third animal—a juvenile—circling from behind. “We assumed we were going to be eaten,” he said. Out of rocks and grabbing branches, they kept shouting and backing away until the cats faded into timber. They later photographed a temporary trail sign warning of lion activity.
Authorities say two hikers discovered the woman’s body around 12:15 p.m. Thursday on a remote stretch of the trail south of Glen Haven, about 7 miles northeast of Estes Park. The hikers reported seeing a mountain lion near the victim and tried to scare it by throwing rocks. A physician in the group checked for a pulse and found none. Colorado Parks and Wildlife officers and Larimer County deputies responded with dogs, a helicopter and ground teams. One lion at the site was shot, fled and was later found and euthanized; a second found nearby was also euthanized. Necropsies are planned to test for disease and to check stomach contents and condition. Officials said a third lion may have been in the area and remained unaccounted for as of Friday.
Other locals described a cluster of recent encounters. Trail runner Gary Messina said a lion rushed him in November on the same mountain. He snapped a quick photo of glowing eyes in brush before the animal charged, he said, forcing him to kick dirt, shout and finally break a bat-sized stick from a downed log. “I hit it in the head and it ran off,” Messina said. Glen Haven resident Kellie Mahoney shared security video showing multiple lions—an adult and apparent juveniles—padding across her yard at night. In October, resident Mary Crone said her 35-pound Wheaten terrier mix was killed during a walk when a lion seized the dog by the neck; she said another lion appeared on a neighbor’s camera minutes later. Wildlife officers said they documented the reports but could not reliably locate the animals before the holiday week.
Colorado Parks and Wildlife spokesperson Kara Van Hoose said officers posted additional warning signs after the November and December reports and returned with hounds when possible. “We’re looking for sign—tracks, scat, cached prey,” Van Hoose said, adding that terrain and winter conditions make lions difficult to find. Without a fresh track or a confirmed DNA link from a bite, she said, investigators cannot say whether the same animals were involved in each incident. The agency estimates Colorado’s mountain lion population at roughly 3,800 to 4,400, most of them secretive and tied to deer ranges. Since 1990, officials have logged fewer than 30 attacks on people statewide, with the most recent fatal case more than two decades ago.
Crosier Mountain rises above the hamlet of Glen Haven, where narrow canyons and steep timbered slopes meet neighborhoods and cabins. The trail network draws hikers year-round from Estes Park and the Front Range. Local residents say lion sightings tend to increase when snow or drought moves deer, or when juveniles disperse. Biologists note that lions are most active from dusk to dawn, though they can be encountered at midday along sheltered drainages. The overlapping reports—Crone’s dog in late October, Messina’s predawn clash in November, and the couple’s confrontation after Thanksgiving—paint a picture of lions using the same corridors in the weeks before the New Year’s holiday.
Larimer County officials said the medical examiner will release the woman’s identity after family notifications. The autopsy will determine cause of death and document injuries, which investigators will compare with tooth and claw measurements from the euthanized lions. Wildlife pathologists will conduct necropsies on those cats to check for rabies or avian influenza and evaluate nutrition and age. Trails leading to Crosier Mountain remain closed with caution tape at trailheads. Colorado Parks and Wildlife said results could guide whether to reopen the area fully or continue targeted searches for any additional lions seen by residents.
Law enforcement and wildlife agencies also reviewed response steps that followed earlier calls. Van Hoose said officers placed temporary signs warning of increased lion activity and returned to canvass neighborhoods. Residents shared videos and photos with officers. Messina said temporary signs were later removed, then replaced after the New Year’s incident. Investigators are compiling a timeline of reports, including the couple’s after-Thanksgiving call, the runner’s November complaint, and the October dog killing, to compare with lion movements documented by tracks and cameras. Any decision on further management actions, officials said, will depend on lab results, confirmed sightings and public safety assessments.
On Saturday, the trail still felt subdued. Wind scoured the ridge above Glen Haven while a sheriff’s vehicle idled near a taped-off lot. Mahoney, the cabin owner, said she has watched more often from her porch since the discovery. “They’re huge,” she said of the cats in her video. Jones said the fatality shook her. “Every single hair on my body rose,” she said, adding that the couple later recognized the warning signs posted at the trailhead. Dieffenbach said he wishes the temporary signs after their encounter had been more specific to the number of lions they saw.
As of Sunday morning, officials said necropsy and autopsy findings were pending, two lions had been euthanized near the trail, and a search for any additional animals continued. The Larimer County Coroner’s Office is expected to release the victim’s name and findings this week, with Colorado Parks and Wildlife planning updates once laboratory results arrive.
Author note: Last updated January 4, 2026.