The state built a bypass around Sheridan and Willamina that opened in 1957 to carry Oregon Route 18 on the south end of the city . The old alignment through the center of town became Oregon Route 18 Business . Sheridan had its largest flooding in history on December 22 , 1964 . The South Yamhill overflowed its banks and isolated the town for two days . The Jesuits sold their training school in 1974 to the Delphian Foundation , who then opened The Delphian School at the site in 1976
largest flooding in history
Christmas flood of 1964
Sheridan, Oregon