All you trail builders and wanna be trail builders will like this. It the government standard Trail Construction and Maintenance Notebook. You can request a copy or download a pdf copy of it. Lots of good stuff in it to learn or refresh your trail building and maintenance skills.
http://www.fhwa.dot.gov/environment/recreational_trails/publications/
As we move forward with SAMBA it is important to educate ourselves, both where we came from and where we are headed. Read, ride, learn and teach.