the explorers first look at yellowstone was the morning of july 16, collecting fossils on one of thee mountainriver, peaks of the gala tin range. they looked south and saw the yellowstone river, winding through the valley in the distance, they knew they had arrived.is th run off from the snowy mountain peaks, yellowstone river is the lifeblood of the park.ree- nearly 700flow miles from end-to-end. it is the longest free-flowing river in america.