http://www.waymarking.com/waymarks/WM15RX Waymarking.com] - "Missoula Flood Glacial Erratic, Tualatin, Oregon" USGS Cascades Volcano Observatory As the west-flowing waters rushed around Rocky Butte, a volcanic cinder cone in the Boring Lava Field, sediments were deposited on the west side of the butte forming an approximately 100 to 150 feet high bar that became Alameda Ridge.