DISTINGUISHED CAREER AWARD: Late Quaternary Climate Change in the San Luis Valley, Colorado: A Succession of Contrasting Environments

The northern San Luis Valley has a combination of climate-change archives that are unique in the Southern Rocky Mountains. The archives result from the juxtaposition of high mountains (altitude 4000+ m) with a deep, detritus-filled, hydrologically closed basin (altitude 2300 m). Although the basin floor today receives only about 18 cm of precipitation per year, it contains the largest wetlands in Colorado, chiefly because of water from the surrounding mountains. In this setting, archives that record temperature (glacial deposits and paleobotanical records of timberline altitudes) complement archives in the basin that record millennial-scale climate oscillations and consequent water-table-level fluctuations. During the last glaciation (Pinedale), outwash was transported far into the basin from adjacent mountains. Thus, Pleistocene glacial deposits are in contact with various Holocene deposits (lake, marsh, wet meadows, instream wetlands, terrace deposits, and eolian strata).

The paleoclimate archives in and near the San Luis Valley record the evolution of a broad range of contrasting environments since the last full glacial. The sequence began at a time when cold-water lakes similar to those in present-day Arctic Canada existed just upwind from the Great Sand Dunes. Then climate warmed and food and water became sufficient to support large mammals (nine mammoth localities) and the largest concentration of Folsom sites in Colorado. After about 8,000 cal yr B.P., climate became more arid, and between about 7,100 and 3,100, eolian sand was deposited over much of the east side of the basin. Between about 3,100 and 1,800 cal yr B.P., climate became effectively wetter and water table rose, causing lakes and wetlands to form and streams to aggrade. Subsequently the water table fell, and since 1,800 cal yr B.P. episodes of eolian sand transport have waxed and waned; today, a small number of dunes migrate through broad areas of stable eolian sand.