Mineralogical and paleobotanical characteristics of the sedimentary fill in a shallow, saline lake in southeastern Alberta indicate that drought intervals are aperiodic and that climatic extremes unprecedented in historic time occurred earlier during the Holocene, when century long intervals of repeated, intense droughts alternated with long periods when droughts were rare. Low-water intervals (signifying periods of drought) are recorded by carbonate-rich laminae containing abundant plant fossils indicative of hypersalinity. In contrast, highstands of relatively fresh water (outlining moist periods) are represented by massive, silicate-rich sediment with lower numbers of halophytic indicators.