PALEOGLACIER FLUCTUATIONS IN THE EASTERN KLAMATH MOUNTAINS, NORTHERN CALIFORNIA

The Klamath Mountains in northern California contain evidence of repeated glacier fluctuations during the Quaternary Period in the form of moraines, cirques, and roche mountonnées. Due to the remoteness of the region, very little research has been conducted on past glacier extents and the exact timing of most of these glacier fluctuations is still not known. To determine the timing of glacier fluctuations, we cored moraine-dammed lakes and analyzed those sediments using loss-on-ignition, magnetic susceptibility, grain size and radiocarbon dating. We extracted cores from two lakes on the eastern side of the Klamath Mountains with different geomorphic relationships to their cirques: Picayune Lake (41.22198°N, 122.52402°W, 1859 m asl) and Middle Deadfall Lake (41.316966°N, 122.503223°W, 2212 m asl). Sediments from Picayune Lake, a small lake (~15 acres), located <300 m from the cirque headwall, indicate that the ice was likely completely gone from the valley by ~13,000 cal yr BP. Middle Deadfall Lake, however, is located ~1,000 m from the cirque headwall and sediments there record a cease in glacially sourced sedimentation also by ~13,000 cal yr BP. These records show that glaciers were retreating during the late Pleistocene just prior to the Younger Dryas cold period and that there is no evidence in these valleys for ice pausing or re-advancing during the Younger Dryas. Although the cirque above Middle Deadfall Lake contains mostly ground moraine and kettle lakes, there may be evidence in the near-surface lake sediments for a re-advance during the Little Ice Age. Analysis of near-surface sediments is forthcoming and will help elucidate if these paleo-glaciers re-advanced during the late Holocene.