After issuing a challenge to @Diamond, I was smacked with the challenge below. No progress yet, but posting it here is the first step...

1. Eons ago, mankind settled the red planet, Mars. One of the earliest settled areas was the great Valles Marineris, Mariner's Valley. This massive chasm, almost as wide west to east as the continental United States, was a hotbed of mineral wealth and an ideal location for early sea formation.
2. The terraforming went on for centuries and was eventually successful. Mankind and his genetically engineered servant races spread to the four corners of Mars. But... nothing lasts forever. Eventually, contact with Earth was lost. Nuclear annihilation? Plague? Rogue AI's? No one knows. The civilizations of Mars went on, alone. And then one day, the terraforming began to break down.
3. Let's see a map of a post-Earth Mars, thousands of years from now. Specifically, the Valles Marineris region.
4. At one point this was a huge inland sea emptying into the Great Northern Ocean. There are still some minor lakes and rivers at the canyon's bottom, but for the most part everything has dried up.
5. During the first years and decades of colonization/terraforming, people built on the surface, on the newly fertile lands around the canyon's edges, with mines here and there to extract mineral wealth, but as time went on and the water level began to sink, folks started building lower and lower in the canyon to stay close to the water. They built towns on spires of rock sticking out of the water. They carved cities from the walls of the canyons. Eventually they populated the chasm's floor.
6. Your challenge is to map, in as much detail as you want, the various major (and minor, if you want to) civilizations that have existed through out the canyon's history.
7. You could do a basic top-down view and 'layer on' the various civs that existed in the same area(s) over the centuries, or maybe do a side view to show the sequentially lower and lower settlements. Totally up to you.
8. Don't forget the engineered races that Man brought with him or created on Mars; I'm sure they've got their own proud histories by now...
9. Make sure to include some ancient artifacts and ruins, etc.
10. Sidebars with brief histories are totally optional.