These horses, running wild in herds, had crossed to the upper Plains.

La Verendrye, and later Lewis and Clark, had found the Indians using horses in the north.

The Indians, as we have seen, had learned to manage the horse.

Formerly they had used dogs to drag the travois, but now they used the "elk-dog," as they first called the horse.
In the original cow country, that is, in Mexico and Texas, countless herds of cattle were held in a loose sort of ownership over wide and unknown plains.

Like all wild animals in that warm country, they bred in extraordinary numbers.