The Montrose County sheriff’s office is investigating the death of a 49-year-old woman from Lakewood who collapsed while hiking with her sons in the Black Canyon of the Gunnison National Park late Monday afternoon.

The woman, whose name has not been released, was hiking on the Gunnison Route, southeast of Grand Junction, with her 16- and 20-year-old sons when she collapsed on the trail, according to the National Park Service. One of her sons hiked out to request help while the other stayed with her. The woman had no pulse when rangers arrived.

The woman’s body was retrieved by a fire helicopter staged at Vernal, Utah, officials said. The incident is being investigated as an accident by the park service and the sheriff.

Parks officials said that incident plus another on Monday — in which a hiker became lost after leaving North Vista Trail on the North Rim of Black Canyon — remind visitors to be prepared for backcountry hiking by planning their routes, knowing their physical limits, carrying plenty of water and being “especially mindful of extreme temperatures.”

“Canyon environments, especially those with dark rocks and little shade, are often much hotter than the surrounding terrain,” wrote Sandra Snell-Dobert, spokeswoman for Black Canyon of the Gunnison National Park, in a press statement. “Exertion and heat can be a deadly combination, particularly for those with other health conditions. Park rangers recommend against hiking in the heat of the day. The highest temperatures in the canyon typically occur between noon and 5 p.m.”

The Black Canyon of the Gunnison reached a high of 86 degrees on Monday, according to weather.com.

The lost hiker was fortunate enough to run into a fencing crew, which assisted him in finding his way back, the National Park Service said.