The Code of Federal Regulations (CFR) is the codification of the general and permanent rules and regulations (sometimes called administrative law) published in the Federal Register by the executive departments and agencies of the federal government of the United States.
The CFR is divided into 50 titles that represent broad areas subject to federal regulation. Title 36, Chapter 2 contains laws and regulations that cover all aspects of USFS trails from the NEPA process to illegal trail building.
Want to know exactly where, in Federal Law, it says we can’t just go out and build trails without permission? Here are the two citings that directly address trail building:
§ 261.10 Occupancy and use. The following are prohibited:
(a) Constructing, placing, or maintaining any kind of road, trail, structure, fence, enclosure, communication equipment, significant surface disturbance, or other improvement on National Forest System lands or facilities without a special-use authorization, contract, or approved operating plan when such authorization is required.
§ 261.12 National Forest System roads and trails. The following are prohibited:
(c) Damaging and leaving in a damaged condition any such road, trail, or segment thereof.
PLEASE NOTE: Much of the above has been directly copied from referenced sources publicly available on the internet. Subjective opinion and interpretation can be found in color-hilited text boxes.