This groundbreaking new book captures much of the detailed knowledge of skilled trail designers. It presents eleven generative concepts as the foundation for a concise process that explains, relates, and predicts what actually happens on all natural surface trails. The concepts cover the essential physical and human forces and relationships that govern trailshow we perceive nature, how trails make us feel, how trail use changes trails, how soils and trail materials behave, and how water, drainage, and erosion act.