Yellowstone River tumbling over the Upper falls and falling about 110 feet to the river valley below. . Rocky outcrops form a natural gate through which the water must flow and which constricts the river at the top, but broadens from the tremendous force of the waters impact at the bottom. Plentiful moisture allows trees to grow on top of the rocks as well as shrubs and grasses. These falls are one of the highlights of Yellowstone National Park.