Walker Valley ORV Park is a DNR managed forest near Mount Vernon, Washington consisting of 36 miles of trails for motorcycles, ATVs, and 4x4s.
Official DNR information about Walker Valley can be found here: https://www.dnr.wa.gov/ReiterWalkerValley
The DNR publishes a georeferenced map of Walker Valley: https://www.dnr.wa.gov/geo/walkervalley.pdf
Avenza Maps is one app you can use to load that map. Your location will be displayed on the map. It is available for iOS and Android: https://www.avenza.com/avenza-maps/