This is an 18 mile out and back ride from San Pedro House to the Hereford trailhead. It is a pretty easy ride but is very sandy for several short segments. From the parking lot make your way to the South side of the bookstore (back side of the house). Take the easily marked trail to the South-East stay West of the tree line and ride for about 3/4 mile until you come to a trail running West beside a sandy dry wash. After a short ride you'll see a trail that crosses the wash on the left but stay on the two track heading West. This trail will be where you cross the wash coming back if you decide to make this ride a loop. After 1/2 mile you'll meet the main trail running North/South. Turn left (South) and cross the sandy dry wash. Three miles South you'll come to a sign on the left indicating the Miller Backcountry Camp. Straight ahead there are roadblocks to keep 4-wheel traffic out of Miller Wash. Go ahead and either ride or portage across this sandy dry wash At least it's been dry every time I've been there. After 1 1/2 miles the trail will jog East then cross Hunter wash. There is a trail splitting off here that will take you North back to Miller Backcountry Camp but avoid it. It is a horribly bumpy and sandy trail. Instead cross Hunter wash and proceed South for about 2 1/2 miles. Look for a trail marker on the left. This marks a singletrack trail that is really nice. It will take you under the scenic Hereford bridge and lead to the Hereford trail head where there is a toilet but no water. Return by the same route or turn at the Miller Backcountry sign and follow the single track back to San Pedro House from there.