Glacial Flood Coulee

Glacial Flood Coulee, a photo by teach.eagle on Flickr.

When Glacial Lake Missoula broke its ice dam, the resulting torrent of floodwater created this coulee. Another coulee wall stands two miles to the left of the one on the right. The center island, called Steamboat Rock, was created because its base is hard granite which resisted and split the floodwaters, which then swirled around it, leaving the island of basalt cliffs.

More info about the Glacial Lake Missoula Floods and the Columbia Plateau:
vulcan.wr.usgs.gov/Volcanoes/ColumbiaPlateau/summary_colu...