Many rocks were transported down the Columbia encased in icebergs and deposited from Montana through Idaho , Washington , and Oregon when the flood waters receded and the ice melted .
These large floods altered the landscape of the Columbia River valley and flooded the Willamette Valley .
Many rocks were transported down the Columbia River encased in icebergs and deposited from Montana through Idaho , Washington , and Oregon when the flood waters receded and the ice melted .
These large floods altered the landscape of the Columbia River valley and flooded the Willamette Valley .