If you want to stroll through the only forest on Alaska's remote Shumagin Islands, you have to wear rubber boots and wait until the tide goes out. In the Shumagins, an island chain that jabs into the north Pacific, the few live trees were planted by people. But along a stretch of beach on the northwest corner of Unga Island, there's a grove that hasn't grown for 25 million years. Wind and water have worn away a large bluff to reveal a forest of petrified tree stumps that appear to be marching into the ocean. Unga is the largest of the dozen or so Shumagin Islands, 570 miles southwest of Anchorage near the tip of the Alaska Peninsula.