If you really wanted a different landscape you could place this on a planet that was colonized by the escapees of this Nuclear war. Perhaps your other creatures were already there thus making mankind an intruder. Just depends how realistic you want to keep things.

There for a while it seemed to me that every time they conducted an underground Nuclear test in Nevada, California would have an earthquake. It may have been coincidence and I'm no expert but I figure if you create shock waves down there you could certainly help along some earthquakes. There is little end to the stupidity of man. We shake our heads at the cultures who did not know better than to toss their refuse off the side of a cliff and thereby made themselves sick but don't we do the same thing with all the crap we drag out into the Ocean and dump? We just have a longer arm that's all. I'll stop there before I get on a roll but basically, I don't have a hard time envisioning man shooting himself in the foot.

If man can find a way to create bombs to level a continent they would and that would cause some plate shifting. So you could just imagine a "better" nuclear bomb and viola you have what you need for your world.