The route, known locally as the River Road, runs along the United States side of the Rio Grande which in Texas forms the international boundary between the U.S. and Mexico.

The road runs from Candelaria through the city of Presidio as well as several smaller communities and former settlements to State Highway 118 in Study Butte near Big Bend National Park.

Eastern portions of the road in Brewster County, however, had several previous highway designations going back to 1939.

Along the remaining 36 miles (58 km) to Presidio, the road passes through the former communities or ghost towns[5] of Chinati, Adobes, Indio,[6] and Ochoa.

[10] West of Redford, FM 170 intersects Casa Piedra Road, an unpaved county route that provides access to the headquarters of Big Bend Ranch State Park and Marfa by way of RM 169.

Just east of Lajitas is the Texas Parks and Wildlife Department's Barton Warnock Environmental Education Center.

The road then terminates at Study Butte 3 miles (5 km) from the entrance to Big Bend National Park.

[16] At that time, SH 118 south of Alpine departed from its present route near Adobe Walls Mountain to Terlingua rather than going directly to Study Butte as it does today.

[20] On July 28, 1955, with construction focusing toward the southeast, the road was extended 5.2 miles (8.4 km) beyond Redford.

[20] With southeastward road-building complete, expansion to the northwest resumed on June 2, 1967 with an 8.5-mile (13.7 km) to Ruidosa.

On June 18, 1996, FM 170 was rerouted on Presidio's north side to follow concurrently along the route of US 67 and Bus.