High Quality Content by WIKIPEDIA articles! Farm to Market Road 170, Farm Road 170, or FM 170 is a 114.6-mile (184.4 km) highway maintained by the Texas Department of Transportation (TxDOT) in Presidio and Brewster counties in Texas. 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 Presido as well as several smaller communities and former settlements to State Highway 118 in Study Butte near Big Bend National Park. The road also passes through the southern portion of Big Bend Ranch State Park.