With the popularity of post-apocalyptic stories these days, I went with a green theme here to simulate how nature could reclaim its glory in a world after people... but still with somewhat of a gloomy atmosphere because it is a world after people.
I played a game called Oblivion once, from the same guys who made Fallout. Too addicting for my own good, I think I've already mentioned that Fallout was the last game I played regularly Anyways, here's a link from the National Park Service which breaks down the history of Great Falls in a table timeline. I would usually look on wikipedia for this kind of stuff, but the Park link seems to provide more details.
You know it's funny, after I posted that comment I had a sense of deja vu; I am sure this is the second time we've had this conversation after I likened one of your photos to Oblivion (or similar video game)