Washington doctor dies during Grand Canyon rim-to-rim hike at age 74

Grand Canyon Regional Communications Center staff received a report on May 15 of an unresponsive hiker on the North Kaibab Trail, about half a mile below the North Kaibab Trailhead.

Though there is limited cell phone service in the canyon, the incident happened close enough to the top that they were able to call for a park service helicopter. Medics restarted his heart, but it later stopped again, and he was pronounced dead at the scene.

His cause of death is under investigation by the Coconino County Medical Examiner's Office, according to the park service.

Fellow doctor, Tom Helpenstell, who worked with Smith for more than 30 years, told Fox News Digital the pair ran across the canyon when it was hotter, and he believes it was a "freak" accident.

"We worked together in the same office and assisted each other every Tuesday in surgeries for 30 years," Helpenstell said. "He and I have run across the Grand Canyon three times, doing Ultra Trail-type running. Probably two years ago, he decided not to do running [anymore], so he was hiking with a group out of Tucson, Arizona, where he spends the winters."

Before deciding not to keep running, the pair ran up Mount Whitney together, completed full Iron Man competitions and Olympic-distance triathlons together, and climbed Mount Rainier.

"He's super active, super fit," Helpenstell said. "This was not even a run, this was a hike. I don't want to downplay it. Grand Canyon's a big day, for sure, but this was completely out of the blue."

In addition to Smith's athletic feats, Helpenstell said he was highly respected in his community for his work in general orthopedics, where he did trauma, hip and knee replacements. 

"He read like crazy," Helpenstell said. "He was like an encyclopedia. We would always joke, we don't need Google, we have Dennis. He was really into health and nutrition, and what diets are the right ones to take, and what supplements. I mean, the guy was crazy about staying healthy. He had switched to playing pickleball because he thought it would make his brain learn new things, which would keep him from getting Alzheimer's or anything like that. He was more focused than anyone I know about staying healthy and living long, which makes this hard."

Smith leaves behind his wife, Evelyn, who would have celebrated their 50th anniversary on Sunday, and four children. 

He also leaves behind numerous grandchildren who he enjoyed hiking and running with.

"Be aware that efforts to assist hikers may be delayed due to limited staff, the number of rescue calls, and employee safety requirements," according to the park service.