The following information is provided in addition to the original article, IMBA Update: Working With the National Park Service – Interview with Jenn Dice, that appeared in Dirt Rag issue #138.

List of 44 National Parks with dirt trails and dirt roads open to mountain biking:
http://www.imba.com/resources/agencies/nps_dirt_roads.html
http://www.imba.com/resources/agencies/nps_dirt_trails.html

Check out IMBA’s site for more information about Take a Kid Mountain Biking Day, October 4th.

Of the 100 plus events that have been registered for the day, three are specifically on National Park land:
Valley Forge National Park
Fort Dupont National Park
Golden Gate National Park