The flood of December 1964 in the redwood areas of north coastal California was the most damaging in the history of the area. The flood resulted from a series of storms in late December, but primarily from the warm torrential rainfall of December 21-23. This rainfall reflected the combined effect of moist unstable airmasses, strong west-southwest winds, and mountain ranges oriented nearly at right angles to the flow of air. The magnitude of the rainfall over much of the mountainous area was equal to or greater than that estimated to have an average return period of 100 years. Precipitation totals in excess of 10 inches in 24 hours and 15 inches in 48 hours were commonplace in the mountains and interior valleys. The peak discharge of streams draining these drenched areas was extremely high and also had a return period estimated to be greater than 100 years. By contrast, some of the areas immediately adjacent to the Pacific Ocean had maximum 24-hour rainfalls of only 2 inches and the small streams draining these low-altitude basins experienced rises that were little greater than those that occur during the usual winter storms.
