An old lava flow changed the geologic structure of this area and created a multitude of famous springs. Over thousands of years, volcanic activity repeatedly spread lava over the Snake River plain, slowly forcing the river southward in a great curve. Successive channels of the river and its tributaries were filled with spongy lava and became both reservoirs and underground conduits gathering water from far to the northeast. Torrents from one or more of these buried channels burst forth on the opposite canyon wall.