A hiker was found unresponsive at Zion National Park Friday and later pronounced dead, according to the National Park Service.

The 63-year-old man from San Diego was found on the West Rim Trail near Scout Lookout after park rangers received a report of an unresponsive hiker in the afternoon.

Rangers hiked to the man with medical equipment, including an automated external defibrillator (AED) and a heart monitor. Visitors with emergency medical training were performing cardiopulmonary resuscitation (CPR) on the man when the rangers arrived.

“After nearly an hour and a half administering CPR, treatment with the AED, and checking their condition with the heart monitor, the park consulted with a doctor (medical control) and the patient was pronounced dead,” the NPS said in a news release.

The hiker, who was not identified by authorities, appears to have experienced a heart attack, according to the NPS. His cause of death is under investigation by the Washington County Sheriff’s Office, the Utah Office of the Medical Examiner and the NPS.

“All of us at Zion extend our deepest condolences to this hiker’s family,” said Jeff Bradybaugh, superintendent for Zion National Park. “We also want to express thanks to the bystanders who assisted by performing CPR.”

The effort involved over 20 search and rescue team members, emergency medical technicians, paramedics and the park’s ambulance.

The West Rim Trail was reopened after it closed for rescue operations.