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The floods of December 1955-January 1956 in the Far Western States were in many respects the greatest in the area in the history of recorded streamflow. One outstanding feature of the floods was the unusually large area involved the western one-third of Nevada, the northern two-thirds of California, the western half of Oregon, one-third of western Idaho, and minor parts of Washington. Other outstanding features were the record-breaking peak discharges in much of the flooded area and the extensive flood damage. The loss of 72 lives was attributable to the flood and total damage amounted to about $190 million. The floods were caused by a series of storms from December 15 to January 27; three occurring between December 15 and 27 and three more from January 2 to 27. In all but a few areas the storm of December 21-24 was the most severe. The storms all reflected the effect of the combination of a moist, unstable airmass, strong west-southwest winds, and mountain ranges oriented nearly at right angles to the flow of air. The unusual feature of the storms was the persistence of the strong flow of moist air. The major storm of December 21-24 was accompanied by high temperature and high wind velocities. As a result, a considerable amount of the snow which had accumulated at higher altitudes was melted. This snowmelt, added to the heavy precipitation at lower altitudes, caused record-breaking runoff in the streams draining the Sierra Nevada, in Idaho, and in Washington. The coastal areas of northern California and southern Oregon had measurable rainfall on 39 of the 44-day period between December 15 and January 28. At several stations the recorded precipitation for the months of December and January exceeded 60 inches. Flood runoff in the streams not affected by regulation exceeded any previously recorded throughout much of the area. Some rivers that had particularly notable floods are: the Carson River, in the Great Basin, where the peak was nearly twice that of the record flood of 1950; the San Lorenzo River, in central-coastal California, which flooded the city of Santa Cruz; the Kaweah River, in the San Joaquin Valley, where the flood peak of December 23 was almost double the record peak of 1950, and which flooded the city of Visalia and the towns of Farmersville and Three Rivers; the Feather River, in the Sacramento Valley, where a levee failure flooded Yuba City and caused the loss of 38 lives; the Klamath River, in north-coastal California, where the peak discharge of 425,000 cfs at the gaging station near Klamath, Calif., was one and one-half times greater than the peak of record and was exceeded only by the legendary floods of 1861-62; the upper Boise River where the December 23 peak equaled the maximum during Al A2 FLOODS IN FAR WESTERN STATES 45 years of record; the Willamette River and many of its unregulated tributaries where the peak discharges were about equal to any previously recorded; and the Rogue River in coastal Oregon, where the peak flow of 414,000 cfs below the Illinois River near Agness was as high or higher than any flood in the last 65 years. This report presents a general description of the December 1955-January 1956 floods, details and estimates of the damage incurred, and a summary of peak stages and discharges and comparative data for previous floods at the 788 sites. Also included are a discussion of the storm precipitation during the 2-tnonth period, tables of flood-crest stages along the main stem and major tributary channels of the San Joaquin, Sacramento, and Eel Rivers in California, a discussion of flood regulation by storage reservoirs, and a summary of, and comparison with, previous floods. Flood-frequency tabulations and curves are presented for selected gaging stations. INTRODUCTION During the last 2 weeks in December 1955 and during January 1956 the Far Western States were subjected to the greatest floods in the history of recorded streamflow in the area. Intense flood-producing rains fell in about two-thirds of California, one-half of Oregon, onethird of Nevada and Idaho, and minor parts of Washington. The areas of severe flooding are outlined in figure 1. As a result of the flood, 72 lives were lost, and the direct property damage was about $190 million. In addition, there was an incalculable amount of indirect damage due to reduced crop production; losses in business volume, salaries and wages; traffic delays and rerouting; reduced tourist trade; and losses in other intangible items affecting the general welfare. The largest concentration of damage was at Yuba City, Calif., where 38 persons were drowned and property damage exceeded $40 million. The principal storm period extended from December 15 to January 27, with intermittent intense storms throughout most of the area. The storm of December 21-24 was the most intense and caused the highest flood peaks. However, the streams were at or near flood stage during most of December and January. Additional storms occurred after January in some parts of the area, but the resulting floods were not as large as the ones in December and January. Because of the severity and the large area flooded all agencies involved in the collection of hydrologic data increased their efforts toward the collection of data for this report. However, it was obvious that additional help would be needed. By the first week of January experienced technical help had been detailed to the flooded area from all parts of the United States to assist in the collection and preparation of these data. The coverage of the data in this report is much more extensive than it would have been without the all-out effort. Included in this report are: a discussion of the precipitation during the period; a description of the floods; information on flood damage; PART 1. DESCRIPTION A3 FIGURE 1. Map showing areas of severe flooding during December 1955-January 1956; the hydrologic regions used in this report; and the range in numbers of the flood-data sites in each region. a table summarizing flood stages and discharge; information on floodcrest stages; a discussion of the effect of storage regulation; and a summary of previous floods at selected sites. Station descriptions and A4 FLOODS IN FAR WESTERN STATES data on stages and discharges at stream-gaging stations and miscellaneous sites are given in Water-Supply Paper 1650-B. To facilitate presentation of the data, the area of severe flooding has been subdivided into eight subareas or hydrologic regions, as outlined by the heavy dashed line shown in figure 1. These regions are : The Great Basin, central-coastal California, San Joaquin Valley, Sacramento Valley, north-coastal California, west-central Idaho, Willamette Valley, and coastal Oregon. In addition, data are included for minor areas under the heading "Areas of minor flooding in Oregon, Washington, and Idaho." The items included in this report are discussed individually for each of the hydrologic regions. This arrangement will enable the user interested in one region only to readily obtain the information on that region. The site numbers at which data on stages and discharge were collected in each region are shown in figure 1. The sites are numbered in downstream order and follow the sequence of parts used in the Geological Survey "Surface Water-Supply of the United States" published annually, starting with Part 10 and continuing through Part 14. Gaging stations, reservoir stations, and miscellaneous sites are included. The same identification numbers are used throughout this report. The exact location of each site is shown in detail on the map included with the description of floods for each region. In the past there have been other notable floods covering parts of the area described in this report for which special reports have been prepared. The Geological Survey water-supply papers in which the information on earlier floods is published are: for western Nevada, Water-Supply Papers 843 and 1137-H; for central and northern California, Water-Supply Papers 843, 1137-E, 1137-F, 1260-D, and 1320-D; for Oregon, Water-Supply Paper 968-A, 1080, 1137-E, and 1320-D; for Idaho and Washington, Water-Supply Paper 1080. The historical data found in these earlier reports are not included in this report. A preliminary report entitled "Floods of December 1955-January 1956 in Far Western States" was published in 1956 as Geological Survey Circular 380. It consists primarily of a tabulation of peak discharges in the same area included in this report. ACKNOWLEDGMENTS Collection of field data necessary for the computation of peak discharges by indirect methods was materially implemented by technical personnel of the Surface Water Branch detailed to the flood area. In addition, personnel for surveying parties were made available by the California Department of Water Resources, the Corps of Engineers, Department of the Army, and the U.S. Bureau of Reclamation. PART 1. DESCRIPTION A 5 Sources of the data are specifically acknowledged where they appear in the text. Although too numerous to mention individually, acknowledgment is made to the many individuals, corporations, and governmental agencies who furnished assistance and data for this report. PRECIPITATION The flood-producing rains of December 1955 and January 1956 in California, western Nevada, Oregon, and Idaho, and scattered basins in southern Washington were without precedent when considered in the light of total area affected and volume and duration of precipitation. The principal storm period from December 15 to January 27 was ushered in by two minor storms in early December, which produced conditions favorable for subsequent high runoff. Between December 15 and 27 there were three distinct storm periods, and three more occurred from January 2 to 27. In all but a few areas the storm of December 21-24 was the most intense. The storms were associated with frontal passages and were generally centered over northern California. The storm

Floods of December 1955-January 1956 in the far Western States, Part 2, Streamflow data