** ADVANCE FOR MONDAY, JULY 23--FILE **Appalachian Trail thru-hikers Phillip Zappone of Shrewsbury, Mass., left, and Brodie Trickey of Greenville, Tenn., pause near the summit of Mount Katahdin to look back at the land they covered after a five-month, 2,155-mile hike, in this Sept. 7, 2001, file photo, in Maine's Baxter State Park. Henry David Thoreau made his third and final trip to Maine's North Woods 150 years ago, traveling waterways and forests that shaped so many of his ideas about nature. (AP Photo/Robert F. Bukaty/FILE)