35° 12' 39.5" N 107° 44' 33.8" W (WGS84) (Google Maps)

Cibola National Forest

At this locality, one can find small topaz and garnet crystals within light-gray to pink-gray rhyolite. These minerals were presumably deposited from the vapor phase and are therefore found in vesicles in the host rhyolite. The garnets are generally a millimeter or two in diameter, and the topaz crystals are generally a millimeter thick and about half a centimeter long. Look for the most vesicular rhyolite and break those blocks open with a hefty sledge. The map below shows the distribution of the host rhyolite (purple hatching) in the area around the given coordinates, which are for a convenient parking pull-out. Head up the hillside and bust open some rocks!

East Grants Ridge - A Mineral Potpourri (New Mexico Geological Society)

Gem Trails of New Mexico, James R. Mitchell

A quick Google search will turn up many more resources about this site.