Stream - 376The Rio San Antonio heads on the Valles Caldera and flows south into the Santa Fe National Forest. The river is mostly meadow in this upper portion and roughly follows FR376 south and then east along NM126 and then south along NM 4 where it joins with the East Fork at Battleship Rock to form the Jemez River. The river along NM 4 rapidly descends in altitude and consists of pocket water and plunge pools.

The Rio San Antonio is mainly a Brown Trout fishery but is stocked regularly with Rainbows at San Antonio Campground, La Cueva Picnic Area and along some of the bridges in La Cueva.