From San Ysidro, take NM 4 and then turn left on NM 385, which becomes FR 376. Continue past the Gilman Tunnels. At Porter Landing, the road crosses the Rio Guadalupe to follow the Rio Cebolla. Just beyond Porter Landing, pull off and park at 35 deg. 49.455 min. N, 106 deg. 47.225 min. W (7280 feet).
To begin the hike, cross the road and follow former FR 604 as it heads northeast up Schoolhouse Canyon. This old road is closed to vehicle traffic but makes a great hiking trail. In the upper part of the canyon you will pass through the south edge of a large clearing from a fire. At the top of the canyon is a small and ephemeral pool of water, no doubt appreciated by the local animals.
Just beyond the top of the canyon, at 35 deg. 49.969 min. N, 106 deg. 46.228 min. W, you will encounter a gate in the barbed-wire drift fence enclosing the mesa top. Beyond this gate the terrain is gently rolling and fairly open, giving you license to explore in any direction you want. One option is to hike along the various mesa-top roads, then cut to a mesa edge for lunch with a view. Then it's back to the gate for your hike down Schoolhouse Mesa and back to the car.
Once you're on Schoolhouse Mesa, you're back in vehicle country. Please consider taking along a trash bag, and cleaning up after less careful users of the national forest.
A shorter version of this hike will get you entirely off the beaten path. As you hike up Schoolhouse Canyon, at about 35 deg. 49.624 min. N, 106 deg. 46.748 min. W you'll notice that the terrain off to your right (south) forms a bench partway up the tip of Schoolhouse Mesa. Leave the former road and work your way south in order to explore the bench. You'll have no problem finding a lunch spot with a pretty view of the canyon below.