A woman died while hiking in western Colorado on Monday as a heat dome blanketed pockets of the American West and drove up temperatures in a number of states. Marsha Cook, from Cedar Rapids, Iowa, was pronounced dead after collapsing around the two-mile mark of a hiking trail at Colorado National Monument, officials said Wednesday. She was 54.

Mesa County Coroner’s Office will investigate Cook’s death and determine what caused it, the National Park Service said in a statement. Although officials did not share more information about the circumstances around her collapse, they warned other people visiting the monument to be aware of excessively high temperatures in the area during the summer season and the potential dangers of those warm conditions for human health, especially when participating in an outdoor physical activity.

“Hiking in hot weather can lead to serious health risks including heat exhaustion and heat stroke,” the park service said in its statement about Cook’s fatal hike. “Daytime temperatures in Colorado National Monument have exceeded 90 degrees in the past week, and hot weather is expected throughout the summer.”

Anyone planning to hike at the Colorado National Monument should either do so early in the mornings or late in the afternoons — finishing before 10 a.m. or starting after 4 p.m. — to lower their exposure to the heat, according to the National Park Service.

Park officials said their staff received a report at about 2:30 p.m. on Monday that a woman collapsed and lost consciousness while hiking the Lower Monument Canyon Trail. She collapsed roughly two miles into the hike, which is a loop that runs for about five miles. The park service describes the difficulty level of that hike as “moderate to steep” and notes in the description that completing the full loop generally takes hikers between four and six hours.

Multiple agencies responded to the scene where Cook collapsed, including park rangers, state wildlife officers and fire officials, as well as search and rescue crews from the surrounding counties, the park service said. The hiker’s family along with first responders attempted life-saving measures like CPR, but she was ultimately pronounced dead on the trail.

Located in the semi-arid desert landscape of western Colorado, near the Utah border, the Colorado National Monument draws hikers, campers and wildlife enthusiasts from across the country to see its monoliths and red rock canyons. The national park and broader region have experienced an extreme heat wave recently, with meteorologists issuing various heat watches and warnings for parts of Colorado this week as temperatures soared. 

While Denver set a new heat record on Wednesday, the National Weather Service noted that above-average temperatures in the counties surrounding the Colorado National Monument could reach triple digits on Thursday. The weather service said conditions in that area could pose “major” health threats to “anyone without effective cooling and/or adequate hydration.”