CASCADE RANGE, OR — A sense of awe swept through the hiking community this weekend as yet another rock stack met its dramatic end—this time at the foot (literally) of a mysterious figure some are beginning to call The Cairn Slayer. Witnesses say the man appeared out of the fog along the Pacific Crest Trail, wearing a weathered flannel, trail-worn boots, and a silent determination. Without a word, he sprinted toward a freshly constructed rock stack, leapt into the air, and unleashed a flying...