" In the spring of 2015, Warren started the Appalachian Trail in Georgia. At age sixty-five, he was a walking contradiction. His white beard clashed with his youthful eyes, his soft, round stomach opposed his rectangular rack-solid calves, and his welcoming smile conflicted with his focused gaze. A finish in Maine would mark his eighteenth thru hike of the 2,189 mile footpath. The circumference of the earth is 24,903 miles; Warren had recorded over 36,000 miles between Springer Mountain and Katahdin. "
― Jennifer Pharr Davis , The Pursuit of Endurance: Harnessing the Record-Breaking Power of Strength and Resilience