The Piedra River is formed by the confluence of its East Fork and Middle Fork, deep in the
San Juan Mountains. The Middle Fork, larger of the two, rises in a bowl-shaped valley in the
San Juan National Forest. It flows southwards, and forms the Piedra after a journey of . The East Fork starts at a small unnamed lake in the
Rio Grande National Forest and flows southwest for about . The Piedra flows through open meadows, then drops into a canyon, receiving O'Neal Creek from the left and Williams, Weimuche and Sand Creeks from the right. The river angles to the southwest and receives the First Fork Piedra River from the right, and after the confluence, flows more in a southerly direction. It receives Heffin and Yellowjacket Creeks, both from the right, and at the confluence with the latter, flows past the town of
Piedra and crosses under
U.S. Highway 160. Its canyon widens into a valley, and flowing south-southeast alongside a ridge, the river receives Devil Creek from the left and receives
Stollsteimer Creek from the left at
Stollsteimer. The river then angles southwest, now running alongside
State Highway 151. It enters
Navajo Reservoir near the town of
Arboles, near the
New Mexico state line. Its confluence with the San Juan River, inside
Navajo State Park, is drowned under the waters of the reservoir. ==See also==