X-ray powder diffraction (XRD) analysis of clays from anthropogenic Late Holocene reservoir sediments can provide a paleoclimatic proxy. Illite and smectite are climate sensitive clay minerals and their relative amounts correlate with climatic episodes. Relative percent composition of clays in Late Holocene reservoir sediment is diagnostic of different mineral source areas and their hydraulic transport processes, which are climate controlled. Climosequences of clay minerals from Late Holocene reservoir sediments are correlative with magnetic susceptibility records and provide a relatively simple and cost-effective tool for gaining insight into paleoclimate.