Over a hundred miles of dirt roads and many additional miles of single track trails are open to mountain bikers. Some trails near headquarters are closed. Ask for a bike map at headquarters. You must stay off these trails even if the signs are hidden by grass or are missing. All single-track trails are closed for 48 hours after a half inch of rain.
Roads remain open all the time.
But, up to 48 hours after at least a half inch of rain, single-track trails are closed to bikes to prevent excessive erosion and trail damage. Check at the Visitor Center when you pay your fees. Riding cross-country is never allowed. The backcountry is open to bike campers. Motorcycles and motorized bikes are not allowed.