Prepared for The National Park Service, United States Department of Interior, Yellowstone, Wyoming / The goal of this investigation has been the reconstruction of past seasonal climate for the period 1750-1910 (161 years) in the Yellowstone National Park region based upon tree-ring data. Tree-ring series are useful in the reconstruction of past climate owing to the availability of large numbers of trees, the great longevity of trees, and the critical fact that the climatic information they contain is accumulated over specific years. In this project a number of tree-ring series from the region around Yellowstone National Park have been calibrated against short-term (1912-1971) seasonal temperature and precipitation data for Bozeman, Moran, Red Lodge, and Yellowstone Park. From these calibrations, long-term seasonal temperature and precipitation records have been reconstructed for each of the four stations. A major reason for these reconstructions has been the need for long-term climatic data that can be used to indicate potential variations in the climate of the park region. Knowledge of these climatic variations may facilitate estimates of natural food supplies or availability of forage in winter as related to snow depth. Previously such estimates have had to be based upon relatively short-term climatic data which undoubtedly do not encompass all possible climatic variations. With this in mind, a series of precipitation and temperature maps have been produced to indicate some of the seasonal extremes that have probably been experienced since 1750 within a given year or group of years as indicated by the tree -ring data. It is hoped that these maps will be useful to various types of researchers involved in planning within Yellowstone National Park.