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130 habitat in the United States, their great trails were north and south trails. The rivers flowing mainly east or west into the Mississippi are crossed usually at right angles by the more important trails of the buffalo. The annual movement was caused not so much by the change of temperature (though buffaloes which remain sometimes in cold climates seek the warmer, secluded spots) as by the frozen condition of the ground and the depths of snow which buried the grasses upon which they fed. When, from various causes, the annual north and south migrations of the buffalo herds of the Far West were discontinued, an east and west migration took place—the herds moving westward to more protected portions of the country. As late as 1872, hunting parties made their headquarters during the summer at Hay's City, and in winter moved their quarters a hundred or a hundred and fifty miles westward of their fall camps; near Hay's City the grass was buried under ice and encrusted snow, while near Ellis the ground was bare. Thus unnaturally the migrations were turned east and west rather than north and south, and the trails