The Precipitation Frequency of the Western United States publication is an eleven volume set held in the archives. It was the culmination of many years of investigation and was based all of the previous work on precipitation- frequency studies until that time. It also replaced U.S. Weather Bureau Technical Paper No. 40 for the eleven western states. The states/volumes are: 1 Montana 2 Wyoming 3 Colorado 4 New Mexico 5 Idaho 6 Utah 7 Nevada 8 Arizona 9 Washington 10 Oregon 11 California Each volume is organized into three parts. The first section discusses the historical background, procedures, and methods used in preparing the maps and how to interpret and use them. The second discusses ideas that are applicable only to the particular U.S. state considered in that volume. Included in this section are methods (monograms and equations) useful for estimating precipitation-frequency values for durations other than 6 and 24 hours. The last part of the atlas presents isopluvial maps for the 6 and 24 hour durations for return periods of 2, 5, 10, 25, 50, and 100 years.