From the Badlands National Park website FAQs:
Why is it called the Badlands?
The Lakota people were the first to call this place "mako sica" or "land bad." Extreme temperatures, lack of water, and the exposed rugged terrain led to this name. In the early 1900's, French-Canadian fur trappers called it "les mauvais terres pour traverse," or "bad lands to travel through."
My son Garrett & I spent 3 nights at Badlands National Park on the way back to Colorado from Wisconsin last week. I hadn't been to the park for about 30 years but still recognized the multi-hued, Kodachrome-friendly clay hills and gullies as old acquaintances. Beyond the inspiring rugged scenery, the park is famous for the world-class fossil resources found within its boundaries, particularly late Eocene and Oligocene mammal fossils along with other fauna from ca. 40-28 million years ago.
What I didn't really remember from my teenaged visit but immensely enjoyed on this trip was the park's horizon-spanning mixed-grass prairie habitat surrounding the barren areas most visitors frequent. With so much pristine habitat (the park encompasses 244,000 acres), native wildlife is sure to abound and in my opinion this is the park's best kept secret (though I'm sure my SD buddies are all over the birding there!)
Near-constant companions of the bison, Brown-headed Cowbirds are a bit less charismatic and a lot less mega but I think them not too odious when they are in their natural milieu instead of, say, laying eggs in a Kirtland's Warbler nest.
Western Meadowlarks were also legion in the park, nice to see for a species that has declined across most of its range due to prairie fragmentation and habitat loss.
Anyway, if you are transiting the northern Great Plains I'd highly suggest blocking some time to spend birding and soaking in the prairie ambiance and scenery at Badlands National Park!