Its total length is approximately 12.6 miles (20.3 km).

NM 91's southern terminus is south of Puerto de Luna where the state maintenance ends and it continues south as Paseo del Sol.

It crosses the Pecos River in Puerto de Luna, then heads north into Santa Rosa.

Its northern terminus is at Historic US 66 (Interstate 40 Business/U.S.

The entire route is in Guadalupe County.