There were 3 bustle eras, with an “in between”…

.. when light understructures and draping slimmed down the silhouette for about 3 years.  The “natural form” era between the mid-1870’s 1st bustle era, and the 2nd one only looked good on long, tall, lean, and young women, so didn’t last very long, although this is the style most often depicted in movies and shows about the “Wild West”.