Texas State Highway 118

Texas State Highway 118 in Brewster County, approaching Terlingua and Big Bend National Park

The section of SH 118 within Brewster County makes up a majority of the route's length at 89.7 miles (144.4 km).[17] 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. Although the area around Study Butte is mountainous, the route through much of southern Brewster County is composed of long, straight stretches through arid ranch land as the road slowly climbs in elevation as its distance from the Rio Grande increases. Between Study Butte and Alpine, there are no major intersections, only junctions with unpaved county roads serving ranches and roads into remote residential subdivisions.

Beyond a roadside picnic table near Crossen Mesa past the entrance to Elephant Mountain Wildlife Management Area, the road begins to enter the Davis Mountains. The road then becomes winding as it passes through the mountainous terrain. In this portion, there is another group of roadside picnic tables with a view of Cathedral Mountain. The road at one hill near Alpine has tight turns and steep grades as the road approaches the plateau where Alpine is situated. There is a U.S. Immigration and Customs Enforcement checkpoint south of Alpine.

The road enters Alpine as South Walker Street passing along the eastern edge of Alpine Hill. SH 118 then makes a left and right curve to move one block further west on South Cockrell Street to pass along the western side of Sul Ross State University's Jackson Field football stadium. The road then crosses the Union Pacific Railroad and intersects U.S. Route 67 and U.S. Route 90. US 67 and US 90 overlay each other, and their route through the central part of the city passes along two one-way two-lane streets one block from each other. SH joins this overlay, with its northbound route following west on East Avenue E toward Marfa and its southbound route one block south on East Holland Avenue toward Marathon and Fort Stockton. SH 118 leaves the overlay going northward at North Fifth Street. On the city's north side, SH 118 leaves the street grid and intersects State Highway 223, a short highway passing around Alpine's northeastern quadrant to US 67 and US 90 at Sul Ross State University. SH 118 then crosses the South Orient Rail Line and passes by Alpine Casparis Municipal Airport before leaving town following a straight stretch to the county line.

View of Davis Mountains from SH 118 at Mt. Locke with downhill section of SH 118 at left

SH 118 passes through Jeff Davis County for 66.2 miles (106.5 km).[17] As the road enters the county, the road intersects Ranch to Market Road 1837 to the Girl Scouts of the USA's Camp Mitre Peak, then SH 118 enters Musquiz Canyon where the road again becomes winding with occasional steep grades and sharp curves. There is another collection of roadside picnic tables near the ruins of the Musquiz pioneer homestead on the highway's right of way within the canyon. After this, the road emerges from the canyon near the Chihuahuan Desert Research Institute and passes along a plateau toward Fort Davis.

The road enters Fort Davis as Musquiz Drive and intersects State Highway 17 at South State Street. SH 118 then follows SH 17 through town along State St. passing by the entrance to Fort Davis National Historic Site at Lt. Flipper Drive. The road then passes along the eastern park boundary until SH 118 separates from SH 17 on the north edge of town. SH 118 then follows Canyon Drive out of town along the north boundary of the national historic site into Limpia Canyon.

The road then enters Davis Mountains State Park where it intersects State Park Road 3. The road then proceeds toward Mount Locke and McDonald Observatory with many roadside picnic tables between Fort Davis and the observatory. The route toward the observatory has numerous steep grades and tight curves. At Mt. Locke, SH 118 intersects State Highway Spur 78 which proceeds the rest of the way toward McDonald Observatory.

Beyond the observatory at Eppenauer Ranch, the road becomes much more rugged with narrower lanes and only grass shoulders. The road continues through steep grades and curves requiring slow speeds through the forested higher elevations of the Davis Mountains. Along this stretch to the intersection at SH 166, the roadway is often not fenced and cattle guards cross the road. Loose livestock pose a hazard to motorist in this portion of the road. In this section of the road is the Lawrence E. Woods Park in Madera Canyon, a roadside drive with five picnic tables amidst a grove of Ponderosa Pines that is also the trail head of a 2.5-mile (4.0 km) Davis Mountains Preserve hiking trail. After the intersection with SH 166 toward Valentine, SH 118 alternates between straight and mountainous stretches for the remainder of the distance in the county.

The Culberson County portion of SH 118 is the shortest at 1.5 miles (2.4 km).[17] The road continues north through ranch land with no intersections with public roads until it terminates at Kent at the edge of the northern foothills of the Davis Mountains. At its terminus, the road overpasses Interstate 10. Beyond the terminus at I-10, the roadway itself continues northward as Ranch to Market Road 2424.