449' basalt formation resulting from the erosion by the Missoula floods circa 10,000 - 13000 BC
A Cayuse Indian legend offers an alternative explanation of their formation, "Coyote, the Trickster spirit hero of many native stories, fell in love with three sisters who were building a salmon trap on the river near here. Each night Coyote would destroy their trap, and each day the girls would rebuild it. One morning Coyote saw the girls crying and found out that they were starving because they had not been able to catch any fish in their trap. Coyote promised them a working fish trap if they would become his wives. They agreed, and Coyote kept his promise; however, over the years he became jealous of them. He changed two of the wives into these basalt pillars and turned the third into a cave downstream. He became a rock nearby so he could watch over them forever."
The formation has also been referred to as Captains Rock in honor of Lewis and Clark who passed this way on October 18, 1805.