Chasm City was the largest settlement on Yellowstone, easily dwarfing Ferrisville, the second largest. When Americans originally settled the Epsilon Eridani system by Von Neumann robot, the location of Chasm City -- a huge crater spewing unusual gases -- was spotted. The crater's edges granted protection from the wind storms and its gases helped provide a breathable atmosphere for the original colony, and for the city that would come later, which was contained underneath eighteen huge bio-domes known collectively as "The Mosquito Net".
Chasm City became one of humanity's greatest achievements when the Demarchists presided over a golden age known as the Belle Epoque, from roughly 2350 to 2510. During that time, the city itself and the planet's orbiting habitat system -- the Glitter Band -- became a humanity-wide byword for opulence, luxury, and success.
That all changed, however, with the onset of the Melding Plague. As the buildings, implants, and technology that ran Chasm City were disrupted and ran amok, the city as it then existed was effectively destroyed along with its golden age. Humanity survived though, falling back onto long abandoned technology such as steam power, and the city stratified itself into two layers: The Mulch, and The Canopy. The Mulch was a shanty town at street level where the melding plague remained rife (possibly still existent), and The Canopy was a relatively modern retreat in the topmost stratum, where the rich clung to their technologically-enabled lifestyle with the remnants of their nanotechnology.