Grand Canyon National Park officials say a 69-year-old hiker died along the River Trail near Phantom Ranch Saturday.
Scott Sims of Austin, Texas, was attempting to hike to Phantom Ranch for an overnight stay via the South Kaibab Trail when he became unresponsive.
Bystanders attempted CPR and three park paramedics took over once they reached the scene, but Sims died.
The Park Service and Coconino County Medical Examiner will handle the investigation.
Park rangers urge visitors not to hike in the inner canyon between 10 a.m. and 4 p.m. with dangerously high temperatures. Exposed parts of the trail can reach more than 120 degrees during the summer months — even in the shade.