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Dennis is from Inyokern, California and was camping with his parents and sisters at Yellowstone National Park in Wyoming when he disappeared on April 12, 1966. His seven-year-old sister had gotten lost and he and his father were searching for her in the forest when they decided to split up. Dennis was last seen walking away from his wife at the Cascade Picnic Area, a quarter-mile north of Canyon Junction, at 1:30 p.m. His father found Dennis's sister, but Dennis has never been heard from again and an extensive, two-week-long search of the camp turned up no indication of his whereabouts, not even his footprints.
Dennis had prior wilderness experiences from going on hunting trips in California with his father in the past, and knew basic survival skills. He is presumed to have become lost or injured in the wilderness, but it's possible he was picked up by a passing motorist on the park road. His disappearance is considered one of Yellowstone's greatest unsolved mysteries.
National Park Service
by Lee H. Whittlesey