 The section of SH 118 within Brewster County makes up a majority of the route's length at .The route begins where the roadway from Big Bend National Park's headquarters reaches the park's western entrance, and then proceeds a short distance to Study Butte.At Study Butte, SH 118 intersects FM 170 to Terlingua and Lajitas, and then proceeds along the Rio Grande to Presidio.