| Further understanding Holocene hydroclimatic dynamics in the northern Rocky Mountains is important for increasing the accuracy of future climate models. The southern Beaverhead mountain range of western Montana is characterized by an underrepresented, high-elevation and semi-arid climatic state in regional hydroclimatic reconstructions. Sediment deposited in Morrison Lake contains both carbonate minerals and organic material that can be utilized to interpret climatic variability through stable isotopic analysis. The δ18O carbonate mineral record from Morrison Lake shows climatic state shifts throughout the late Pleistocene and Holocene. A majority of the early Holocene shows evidence of a dry climatic state (14,800-11,100 cal yrs.BP). Wet conditions existed during two periods of the late Pleistocene and early Holocene (15,600-14,800 and 11,100-10,000 cal yrs.BP). During the middle Holocene (10,000-6,000 cal yrs.BP),Morrison Lake experienced extremely dry conditions and a lack of carbonate preservation. At 6,000 cal yrs.BP,Morrison Lake shows a transition to a consistently wet climaticstate. Spectral analysis indicates that the most recent δ18O of carbonate sediments (2,300-(-68) cal yrs.BP) show periodicities of 25, 40, 52, 55 and 78-years.Keywords: hydroclimate, stable isotope analysis, carbonate sediment |