Grass farmers have been burning fields , as part of their production , since the 1940s . The smoke is often irritating to residents ; in 1988 it caused a 23-car pileup on I-5 . Over the years , several pieces of legislation have limited the amount of burning permitted . With the passage of a bill championed by legislator Paul Holvey in the 2009 session , burning has been banned since the summer of 2010 , with the exception of an area of about with steep terrain and certain species . ( At its peak in the 1980s , about were burned each year . ) The Willamette Valley is prone to periodic floods . Notable floods include the Great Flood of 1862 , events in 1899 , the Christmas flood of 1964 , and the Willamette Valley Flood of 1996 . Part of its floodplain is a National Natural Landmark called the Willamette Floodplain
Great Flood of 1862
Great Flood of 1862
Willamette Valley