A PRELIMINARY STUDY OF THE LAST GLACIAL MAXIMUM IN THE MOSQUITO RANGE, COLORADO

The Mosquito Range is a north-south trending range bordered by the upper Arkansas River Valley and Sawatch Range to the west and South Park and the southern Front Range to the east. Many peaks exceed 4000 m and features typical of alpine glaciation characterize landscapes at higher elevations. Cirques carved into the higher peaks served as the principal accumulation areas for valley glaciers, however the glaciers were also nourished by extensive but presumably shallow ice fields that developed on broad, gently sloping interfluves. The ice fields also solely supported several small ice lobes. To a large degree, valley glacier systems were interconnected either by virtue of common ice fields and/or pervasive ice divides. In some locations glaciers in adjacent valleys coalesced to form composite termini. Using the accumulation-area ratio method applied to glaciers reconstructed at their the last glacial maximum (LGM) extents, equilibrium-line altitudes (ELAs) are estimated to have been between 3550 and 3650 m. These altitudes are consistent with and further substantiate a previously recognized, statistically significant west-to-east trend of increasing ELAs from the Elk Mountains and continuing through the Sawatch Range to the Mosquito Range, apparently reflecting eastward transport of moisture during the LGM. Degree-day modeling suggests the magnitude of LGM temperature depression was ~7°C, also in excellent agreement with that similarly determined for the nearby Sawatch Range and Elk Mountains. A chronology for LGM glaciation in the Mosquito Range is being developed using ¹⁰Be analyses of moraine boulders.