Wyoming Highway 173 begins its west end at US 20/WYO 789 just over a mile and a half south of Thermopolis.

Named Buffalo Creek Road, Highway 173 travels southeasterly along the south bank of the Bighorn River.

[2] Two-tenths of a mile later WYO 173 reaches its end at County Route 31 (South Yellowstone Road).

The original Four Mile Bridge, which carried Highway 173 over the Big Horn River, was completed in 1928 and was added to the National Register of Historic Places as part of a forty-bridge collection that illustrate steel truss construction.

[2] It was offered for sale by the Wyoming Highway Department in 1987 ahead of a planned replacement.