Here is info on an event in NYC:
NYCMTB, Trips for Kids Metro NY,, IMBA and NYC Parks present the first annual Highbridge Halloween Trick-or-Treat ride. City and neighborhood youth will have the chance to ride a marked and closed beginner-appropriate loop of the Highbridge mtb trails, stopping at various points along the trail to learn and attempt mountain bike skills, while receiving healthy treats in return.
Location: New York City,NY 10040
Event Location: Highbridge Park dirt jump park in upper Manhattan. Fort George Ace. between Amsterdam and St. Nicholas
Event Start Time: 2pm
Event Type: IMBA-affiliated mountain bike club and Trips for Kids
Contact: Jamie Bogner
Contact Phone: 917-478-4228
Contact Email: firstname.lastname@example.org
more info at www.imba.com plus locations all over the world.
also check out the NYC Mountain bike Association