The United States Geological Survey ( USGS ) operates eight real-time stream gages on the Trinity River . The lowermost gage , located at Hoopa , measures runoff from , or 97 percent of the Trinity River watershed . The annual discharge , averaged over the 1964 – 2013 period , was . The average discharge between 1912 – 1960 , prior to construction of Trinity and Lewiston Dams , was . The maximum flow was on December 22 , 1964 during the Christmas flood of 1964 , and the lowest was on October 4 , 1931
Christmas flood of 1964
Christmas flood of 1964
Trinity River (California)