SPRINGDALE, Utah (AP) — A man died of a suspected heart attack while hiking a strenuous trail in Utah’s Zion National Park, authorities said Friday.

The 63-year-old man from San Diego, California, was found unresponsive on the West Rim Trail on Friday afternoon, the National Park Service said in a statement. Other hikers on the trail performed CPR while awaiting the arrival of rangers, who continued CPR and used a heart monitor and an automated external defibrillator to deliver electric shocks in a bid to revive him.

More than 20 search and rescue team members and emergency medical personnel responded to the scene, the statement said. But after an hour a half of resuscitation efforts, the man was pronounced dead.

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

Authorities said the cause of death is under investigation but appears to be consistent with a heart attack.

The medical emergency occurred on near Scout Lookout on the West Rim Trail, which the National Park Service describes as strenuous. The trail was has since reopened after being temporarily closed for rescue operations, authorities said.