Despite huge acreage and treacherous terrain, most missing persons at Yellowstone National Park are found. But a small number of disappearances have never been solved. The reasons why are as vast as the park. =============================================================== Dan Campbell was illegally hunting elk antler sheds in Yellowstone Park when he disappeared more than three decades ago. Campbell had set off from Hellroaring Trailhead to Jardine, Montana, outside of the park's boundaries, with his dog Freckles for a four-day trek. However, when the 42-year-old Montana man failed to appear at the designated location and time, his girlfriend, Tracy Erb, reported him missing April...