Heat stroke and dehydration claimed the life of a Northern Arizona University student who had set off alone in late July for a weekend backpacking trip from a remote North Rim trail in Grand Canyon National Park.

Bryce Gillies, 20, was found by Park Service search crews on July 25, three days after he was reported overdue by his family.

The cause of death was "hyperthermia and dehydration due to environmental heat exposure," according to the county medical examiner's autopsy report.

Hyperthermia, or heat stroke, is an abnormally elevated body temperature, as much as 106 degrees. Heat stroke is the most serious and potentially fatal form of hyperthermia. The two less-severe types are heat cramps and heat exhaustion, according to Web MD. Dehydration occurs when the loss of body fluids, mostly water, exceeds the amount that is taken in.

Combined, the two conditions exacerbate one another.

A person suffering from heat stroke will start to feel confused and disoriented, said Paramedic Pete Walka, a battalion chief with Guardian Medical Transport. They are usually unable to answer simple questions. From those symptoms, the condition progresses to seizures and unresponsiveness.

"In this altered level of responsiveness, if you're by yourself it is very hard to make decisions at that point," said Walka, who wasn't commenting specifically about the Gillies death.

In dehydration, even if you're drinking water, if you're in a hot environment, you're still sweating out more than you can take in. Sweating is the body's main mechanism for cooling itself, and it's natural that you become dehydrated if you're sweating.

"Basically, the environment overwhelms the body's ability to rid itself of heat," Walka explained.

Gillies, a third-year physics major, was found on the top of a 100-foot pour-off in the Bonita Creek drainage area after several personal items belonging to him, including a backpack, were found nearby. His body was less than a quarter-mile away from the Colorado River.

That area is known for its rugged terrain, boulder fields, dry creek beds and steep pulloffs. Summer temperatures easily reach into the 90s above the Rim and exceed 100 below it. Its southwestern facing slopes are exposed to full sun as well, especially in the summer.

According to the coroner's report, search crews found Gillies' backpack containing empty water containers on July 23. The next day, a grocery bag believed to be Gillies' was found. It had a can of tuna and can of beans, both of which had been opened and drained of their liquids. Gillies' body was found the next day, draped over a rock.

The autopsy stated there were no other indications for cause of death. The manner of death was accident, according to Dr. A.L. Mosley, who conducted the autopsy.

Walka said a number of variables determines how quickly someone could succumb to heat stroke and dehydration, such as air temperature, humidity, activity level, a person's hydration level prior to hiking in the Canyon and stress of heat over several days.

It can progress quickly over several hours or over a couple of days of repeated heat stress events, Walka said.

In the classic sense of heat stroke, most people think of elderly folks living in a city with high humidity and no air conditioning.

But there's also "exertional" heat stroke, which usually involves athletes or outdoors enthusiasts, such as marathon runners or football players. Exercising when it is really hot out under prolonged sun exposure can lead to heat stroke in even the most physically fit people.

Gillies, from McLean, Va., was a Wilson Hall resident who, this summer, went to Yua, Ghana, where he worked with the NAU chapter of Engineers without Borders.

Gillies graduated from McLean High School in 2007 and had taken courses at George Mason University. He was an outdoor enthusiast who had hiked the Appalachian Trail and had learned to kayak and to rock climb.

He is survived by his parents, Randy and Warna Gillies of McLean, and a brother, Neal.

Laura Clymer can be reached at lclymer@azdailysun.com or 913-8601.

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