GRAND JUNCTION — Authorities have identified a Colorado National Monument volunteer who died from an apparent heart attack while hiking.

Park rangers say the 72-year-old Bill Karp was hiking on the Monument Canyon Trail with his wife on Sunday. They were about a half-mile away from Independence Monument when Karp collapsed.

Rescue crews tried to resuscitate Karp using CPR and an external defibrillator, but they could not revive him.

Officials say Karp had been a volunteer with the monument's visitors center for about a year and a half.