As others have pointed out the Grand Canyon has the traits of an erosion valley. The western badlands, however, seem to have been formed by a catastrophic flood or floods. Check it out
here (PDF).
I'm a sucker for a pdf, but I don't see any indication in this paper that the "western badlands" were formed by a flood. This paper recounts the evidence for a huge flood caused by spillage from Lake Bonneville into the Snake River. The only topography I could identify was an "upland channel" along the Snake River. ( The overlayed line is 1 mile :)
There is some interesting topography to the southeast of this where the flood entered the Snake River valley, but I believe it is due to subsequent erosion of the deposited material.
"badlands" are typically "dissected terrain," that is an eroded plateau. The badlands of Badlands National Park in South Dakota are an eroded highland between two rivers. Here's a sample, again with a 1 mile reference line:
