In Green River Valley once roamed thousands of bison.

The more arid districts have the fewest large animals, and conversely the more humid the most, though in the latter districts the fauna and flora approach that of the eastern part of the continent, while as the former are approached the difference grows wider and wider, till in the southern lowlands there is no resemblance to eastern types at all.

Once the streams everywhere had thousands of happy beaver, with their homes in the river banks, or in waters deepened by their clever dams.

Otter, too, were there.

The larger rivers are not favourable for fish on account of the vast amount of sediment, but in the smaller, especially in the mountain streams, trout were abundant.