LAS VEGAS (KLAS) — A 31-year-old woman died in Zion National Park during an overnight hike through the Narrows, according to the National Park Service.

The woman’s death — possibly from hypothermia — is still under investigation.

The woman and her husband, 33, began their hike on Tuesday, Nov. 22. Rescuers found the man as he was being helped down the trail by other hikers on Riverside Walk. Other visitors told a shuttle bus driver they had encountered “an injured man and a non-responsive woman” in the Narrows. Rescuers located the woman farther up the trail near the Virgin River. First responders administered emergency aid, but determined she had already died.

The man was transported to Zion Emergency Operations Center.

The couple had the proper permit for the 16-mile top-down hike, but the man told rescuers they became “dangerously cold” overnight and had symptoms of hypothermia.

The man said they stopped about a mile and a half from the north end of Riverside Walk, a paved trail that leads from the Temple of Sinawava to the Narrows. The man said he continued on Wednesday morning to get help while the woman remained behind.

More than 20 search and rescue team members were involved in the search.

The Washington County Sheriff’s Office, Utah Office of the Medical Examiner and the National Park Service are still investigating the woman’s cause of death.