Granted, rocks of certain ages erode out of certain areas more often than others.
New Hampshire for example has been scoured of any significant fossil bearing rock.
Greenland is great for Devonian rocks. Kansas is perfect for Cretaceous oceans while Nebraska is great for Miocene mammals. Some places are good for a wide variety of times.
These are biases of erosion and deposition...
Miocene mammals I've heard of come mostly from the Great Planes, Argentina, East Africa, Europe, India... some from Australia (though I don't have a great knowledge of Australian prehistoric fauna). This new focus on the high Canadian and Greenland islands is just amazing to me.
wa:do