SH 166 facilitated construction of Davis Mountains State Park and the University of Texas at Austin's McDonald Observatory during the 1930s.

[5] The route begins at SH 118 near Nunn Hill approximately 19 miles northeast of Fort Davis.

At RM 505, the highway becomes part of the primary route between Valentine and Fort Davis, the only two towns in the county.

The road's right-of-way is not fenced through many pastures, and loose livestock on the roadway present a hazard to motorists.

Much of the route offers views of Baldy Peak atop Mount Livermore, the highest summit in the Davis Mountains.