The road was to include portions of the present SH 118 and State Highway 166 now known as the Davis Mountains Scenic Loop.

[9][10] With this new designation, the route was largely the same as the present with the exception of taking a more westerly path at a point near Adobe Walls Mountain in southern Brewster County in order to terminate at Terlingua rather than Study Butte; although, except for the stretch between Alpine and Fowlkes Ranch, the road was unpaved and even classified as primitive in places.

[1][15] This extension followed the easternmost path of present-day FM 170 to its terminus, and then down the southernmost stretch of the present SH 118 and the westernmost portion of the current park road ending at the intersection of what is now the Old Maverick Road within the present 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).

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.

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.

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.

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.

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.

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.