In the seven ages of man (The ~10,000 year cycles, not the poem from Shakespeare referring to the Stone/Bronze/Iron ages, but the times in which one age is all but forgotten by the next age.), each time mankind has attained the technology plateau to establish civilization on Mars it has been short-lived. The societal stresses from multiple worlds is something our race has yet still not learned to appreciate. Man still seems to need to control and destroy.
Very few relics of the previous age persist. Even the garbage of the previous age has been lost to time. Very occasionally, we will find a curious relic, such as a spark plug inside of a rock.
Curiously the longest-lasting civilization was during the 3rd Age. Nearly 500 years before collapsing. But then it collapsed with the worst destruction so far. Even the moon shows the scars from that horrible conflict - all the largest patches on the moon are from fusion weapons, not naturally-occurring craters as they would have us believe. Fusion weapons to wipe all trace of there ever being cities on the moon. To return the world to a simplistic agrarian existence until the rise of the next golden age.
Mars is the filter; the filter to see if we have yet reached the evolutionary level to not bicker as small children when in this situation. So far, every time we've made it there, it's eventually led to the falling of civilization once again. Sometimes making it to a higher peak the first time, and others worse.
Why do you think the named the planet after the god of war anyway? Simple: Racial memory.
What else explains Bush wanting to send people to Mars - he's not just betting on a single apocalyptic prediction, the Armageddon legend isn't failsafe. [Just kidding about that one - I hope!!]