The Sioux Ranger District is located in the southeast corner of Montana and the northwest corner of South Dakota. The District is composed of eight separate units of Federal land and has often been described as "islands of green in a sea of rolling prairie."

This is an appropriate description as the Federal lands are hills or mesas of ponderosa pine rising above rolling grasslands. The area offers excellent antelope, mule deer, white-tail deer and turkey hunting. The area is also rich in archeology, paleontology, produces some oil, and supports a sizable livestock population. One of the largest populations of Merlins (a small falcon) known in North America occurs on the District.

There are two classified National Landmarks on the District, the Castles and Capitol Rock. The Castles, located in the Slim Buttes Unit in South Dakota, are a massive limestone uplift that resembles a medieval castle. Capitol Rock, located in the Long Pines Unit in Montana, is a massive white limestone uplift that resembles the Nation's capitol building.