In a rare moment of convenience intersecting road-trip, it turns out my path yielded access to a "bonus" national park. My brother mentioned it at just the right moment, and I was passing within five miles of the entrance.
I made it just before sunset - pretty much the best time to see anything. The canyon was a nice contrast from the orange and reds of the Utah canyons, and it didn't look similar at all. The erosive forces responsible for the black canyon yielded distinctly different shapes in the rocks and cliffs; none of fins of Arches or pillaring of Canyonlands. Instead the brown rocks have more the aspect of crusty loaves of French bread loosely parallel in a huge sack with their nether halves disappearing into impenetrable depths.