To clear this up once and for all with Rockstar's explanation (Yes they did tell us) (if you're a true fan you would have known)
In response to the question posed: With San Andreas being such a huge area, will we get lost in the countryside, and will there be any cars around?
Rockstar: There will be a few 'damaged' versions of cars spawning in several places where gamers would be likely unable to find a vehicle when they need one
Obviously they didnt say that exactly, but it was along the lines of that.
I think it's the Glendale you can see roll down the hill.
Why does it roll down the hill?
Well thats the law of gravity and physics, the car 'drops' from a height onto sloped ground, thus making the car 'bounce' and move forward, gaining momentum as the hill gets steeper.
Why is it damaged?
It's supposed to emulate a wrecked, abandoned car. How can you fail to realise such an obvious explanation.
Please no more on this. Back to the original topic. Of Bigfoot, Who doesn't exist anyway but for the sake of sanity and in the interest of self-preservation I'm allowing it to go on... Stops n00bs complaining that thye arent allowed to believe in ficticious creatures...