The Captains (also known as "The Sisters") are a well-known landmark of the Lewis and Clark Expedition. They are located just downstream from the entrance of Wallula Gap, where the expedition swam their horses across the Columbia on their way home in the spring of 1806. We learned that these features were formed by giant ice age floods that swept almost the whole of Eastern Washington and crashed down the Columbia River many times at the end of the last ice age. They shaped what is now the present Columbia River Gorge. These floods are called the Bretz or Missoula Floods.