First, talk to the local shops and get them on board. I mean really behind the idea. They come into contact w/ MTBers everyday and can really help spread the word. Ask to post flyers at the shop. They have a vested interest in keeping trails open because it creates and maintains customers for them. Gently remind them of this is they aren't receptive for some reason.
Next, organize a preliminary meeting for just the MTB people so you can introduce everyone to what is going on. Again, post flyers. See if one of the local shops will let you hold the meeting there. It brings customers in for them and the setting is right. If not, have it in your back yard. Now, here is the important part:
Get beer and announce this on the flyer. Free beer always brings people out. A 1/4 keg will cost you around $50, some smaller brewers are now doing 1/6 kegs (5 gallons) around $35. Sure, it comes out of your own pocket, but in the long run it will be worth it. If you were a skier, that's less than one day's lift ticket. Also, you might be able to get the shop to split the cost with you. Or, a local micro-brewer might be persuaded to donate a keg.
Alright, you've had the first meeting, people have drank your beer, how do you keep the interest? Organize and lead a weekly group ride. This gets people out, keeps you in contact with them and builds a group of people who have a stake in the new trails. They in turn help spread the word. Offer to start the ride at the local shop to keep them involved.
Also, contact IMBA and get in touch with their state representative.
Good luck.
