Don't do it. This is for the sake of the entire mountain biking community.
Do not go making renegade, unapproved trails on public land. This does nothing but give lawmakers ammunition to ban all mountain bikers from trails. Work through the proper channels to get things approved. If it cannot be approved, look for a private landowner who might be receptive to allowing you to use their property for your recreation. +
Remember- Many states have clauses that protects landowners from liability if they are allowing unpaid recreational use on their land. This protects the landowner and is aimed at encouraging landowners to open access to their property.