Widespread flooding occurred in central California and northwestern Nevada during January 31 - February 1, 1963, as a result of intense precipitation of about 72 hours duration. The flood-producing storm was of the warm type, with precipitation falling as rain at altitudes as high as 8,000 feet. The heavy precipitation, totaling as much as 20 inches or more in the Sierra Nevada, fell on frozen ground or on the sparse snowpack that existed in the higher altitudes. The response of runoff to rainfall was dramatic, as streams throughout the area rose rapidly. Hardest hit were the basins of the American, Yuba, and Truckee Rivers, where flood peaks either reached record-breaking heights or rivalled the discharges attained in the memorable floods of November 1950 and December 1955. Because of the relatively short duration of the storm, the volume of flood flow in 1963 was not outstanding. Ten deaths were attributed to the storm or flood. Preliminary estimates indicate damage in excess of $16 million in foothill and valley areas, but no attempt has yet been made to assess the heavy damage to highways and drainage structures in the mountain areas. The U. S. Army, Corps of Engineirs estimates that its operation of flood-control facilities prevented additional damage of $236 million. Other reservoirs, operated primarily for water conservation or power production, were also instrumental in preventing damage.