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A man who was found semi-conscious after collapsing on a hiking trail in the Grand Canyon over the weekend has died, officials said.

The hiker, identified by the National Park Service as 69-year-old Scott Sims of Austin, Texas, was walking along the canyon’s River Trail and attempting to reach Phantom Ranch, where he had an overnight stay booked. The trail follows the Colorado River and runs for just under two miles, according to the park service.

Sims was reported as being semi-conscious on the trail on Saturday at around 7 p.m. local time, the park service said, and then became unresponsive. Bystanders began CPR and park service paramedics responded, but all attempts to resuscitate Sims were unsuccessful. The National Park Service announced his death on Monday.

The park service did not say what caused Sims’ death, but warned that high temperatures along the trails can pose a danger to hikers. In the summer, exposed parts of the trail can become hotter than 120 degrees, the agency said, and hiking the inner canyon between 10 a.m. and 4 p.m. is not advised.

Help may also be delayed in the summer months because of “limited staff, the number of rescue calls, employee safety requirements, and limited helicopter flying capability during periods of extreme heat or inclement weather,” the National Park Service said.

Sims’ death is the second in the area this summer. CBS News affiliate KLAS reported that a 41-year-old died on the Grand Canyon’s popular Bright Angel Trail on June 16.

About 12 people die each year at Grand Canyon National Park, KLAS reported.

Extreme heat can cause illnesses including heat stroke and heat exhaustion. Heat stroke can cause confusion or loss of consciousness, while heat exhaustion can cause nausea, thirst and heavy sweating, CBS News previously reported. Anyone experiencing these illnesses should call 911 right away and move to a cooler area, drink liquids and otherwise attempt to lower their body temperature.

To avoid heat-related illnesses, the National Weather Service recommends limiting outdoor or intense activity during periods of high heat, and staying in a cool place.

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