Navajo and Apache

Now that the horses were given to the people, and there were a great many people in the land, they commenced to crowd each other. Some of the people wanted to go to war over the slightest thing. They taught their children to be quarrelsome; they were not raising them in the right way. They did not have peace in their hearts. At this time there appeared in the country many plants with thorns, in fact these were more numerous than any other kind of plant. Even the grass became sharp and spiked. It was because of the people's ill nature, and the plants and the grass, that another plan was formed. This time Hasjesjini, the Yei of all the burning minerals in the earth, started a great fire. All the red rocks that we see now burned then. After this the Apache and several other tribes moved eastward. And a number of years after the great fire plants grew again, and this time without thorns. They were better and less harmful.

The Dine' Origin Stories of the Navajo; 1910, Aileen O'Bryan.