A teenager died after experiencing symptoms of heat-related illness while hiking in the Grand Canyon, the National Park Service said.

The teen died Wednesday along a stretch of the Grand Canyon’s Bright Angel Trail, according to the park service. It said in a statement that rangers received reports at around 1:40 p.m. local time that day “of an 18-year-old male experiencing heat-related symptoms” on a portion of the trail deep within the canyon. He had hiked past Havasupai Gardens, a rest stop and campground that already requires a 3,000-foot descent from the canyon rim, according to the Grand Canyon Trust.

Rangers rushed to launch a helicopter rescue operation and ultimately found the teen about 30 feet below the trail, in a remote area, the park service said. They attempted life-saving measures but were unsuccessful.

Officials have not released the 18-year-old’s name, saying Saturday that notifications remained pending to his next of kin.

The park service said the teen had intended to complete a round-trip day hike from the South Rim of the canyon to the Colorado River. That’s the route of the Bright Angel Trail, which the park service says is its most popular hiking trail into the canyon, though it recommends against hiking all the way to the bottom and back in a single day.

“Destinations below Havasupai Gardens are not recommended day hikes due to the long distance, extreme temperature changes, and an approximately 5,000′ (1,500 m) elevation change each way,” the park service’s website said. The site also advises hikers to “check with a park ranger” before attempting to hike to Havasupai Gardens and back in a day, as that trek alone is 9 miles and takes between six and nine hours.

An investigation into the teen’s death is underway at the Coconino County Medical Examiner’s Office, the park service said.

Heat-related illnesses can occur when a person is exposed to extreme heat. The most serious of them, heat stroke, is a medical emergency that can cause disability or death, according to the Centers for Disease Control and Prevention. 

When someone experiences heat stroke, their body’s temperature rises rapidly, potentially reaching 106 degrees Fahrenheit or higher in as little as 10 or 15 minutes, and is unable to cool itself down, the CDC warns. Symptoms of heat stroke can include confusion, slurred speech, loss of consciousness, profuse sweating and seizures.