Palynological data from sediment cores from the Ruby Marshes provide a record of environmental and climatic changes over the last 40,000 yr. The modern marsh waters are fresh, but no deeper than ∼3 m. A shallow saline lake occupied this basin during the middle Wisconsin, followed by fresh and perhaps deep waters by 18,000 to 15,000 yr B.P. No sediments were recovered for the period between 15,000 and 11,000 yr B.P., possibly due to lake desiccation. By 10,800 yr B.P. a fresh-water lake was again present, and deeper-than-modern conditions lasted until 6800 yr B.P. The middle Holocene was characterized by very shallow water, and perhaps complete desiccation. The marsh system deepened after 4700 yr B.P., and fresh-water conditions persisted until modern times. Vegetation changes in Ruby Valley were more gradual than those seen in the paleolimno-logical record. Sagebrush steppe was more widespread than at present through the late Pleistocene and early Holocene, giving way somewhat to expanded shadscale vegetation between 8500 and 6800 yr B.P. Shadscale steppe contracted by 4000 yr B.P., but had greater than modern coverage until 1000 to 500 yr ago. Pinyon-juniper woodland was established in the southern Ruby Mountains by 4700 yr B.P.