John Muir (2015). “STEEP TRAILS: California - Utah - Nevada - Washington - Oregon - The Grand Canyon: Adventure Memoirs, Travel Sketches, Nature Essays and Wilderness Studies from the author of The Yosemite, Our National Parks, A Thousand-mile Walk to the Gulf & Picturesque California”, p.15, e-artnow
Martin Dugard (2011). “To Be a Runner: How Racing Up Mountains, Running with the Bulls, or Just Taking On a 5-K Makes You a Better Person (and the World a Better Place)”, p.7, Rodale