Two quick options.
Head out of town to the north, towards new meadows/lewiston. At lardo's (kind of a old looking restaurant on the left side of the road) Take the warren wagon road turn to the right. Drive up that road until you get to the end. This is the parking lot for sleds. Their are some trail maps there and you can pick your way.
the other option is continue north out of town. A couple miles out you will see a snow park parking lot on the right side of the road. It is before the Brundage Ski area turn. Turn in there and again trail maps and signs.
Good luck Thunder