National Trail Classification System, FSM 2350, and FSH 2309.18, Federal Register: July 3, 2006 (Volume 71, Number 127), Pages 38021-38052 online copy on epa.govArchived 2009-08-07 at the Wayback Machine
National Trail Classification System, FSM 2350, and FSH 2309.18, Federal Register: July 3, 2006 (Volume 71, Number 127), Pages 38021-38052 online copy on epa.govArchived 2009-08-07 at the Wayback Machine