Rescue crews retrieved a missing teenage hiker in Glacier National Park on Monday after a helicopter picked up his heat signature, the National Park Service says.

Matthew Read, 19, had last been heard from on Friday afternoon, when he set out to go hiking in the park. On Sunday, the day he was reported missing, rangers located his car at the Huckleberry Lookout Trailhead. They performed a hasty search that day, and an expanded search followed the next day.

At 11 p.m. on Monday, a helicopter flown by Kalispell-based Two Bear Air Rescue located a heat signature in what the park called “heavily-forested terrain.” The aircraft lowered a rescuer, who found Read lying in the snow, “somewhat responsive.” The crew hoisted out Read and transferred him to a waiting ambulance; the NPS statement described him as being in “stable condition.”

According to the park service, Read had set out on the Huckleberry Lookout Trail, a challenging, 11.6-mile round-trip dayhike to a mountaintop fire lookout tower, when he encountered a snowfield covering the path. Upon trying to cross it, he slipped and fell into a drainage filled with “chest-deep snow,” losing his phone, water bottle, and shoes in the process. Upon realizing that he wouldn’t be able to gain the trail again, Read picked his way down the drainage for three days until the search crew found him.