Stephen C. Porter and Terry W. Swanson
³⁶ Cl dating of the classic Pleistocene glacial record in the northeastern Cascade Range, Washington
American Journal of Science (February 2008), 308(2):130-166

Abstract:
Surface-exposure ages of granodioritic and gneissic boulders on seven successive moraines record the Late Pleistocene history of a major glacier system in the northeastern Cascade Range of Washington. The youngest moraines are boulder-rich and sharp-crested, but successively older moraines have lower boulder frequencies and are more degraded. Seventy-six ³⁶ Cl dates for the moraines cluster in groups having mean ages (+ or -1sigma ) of 12,500+ or -500, 13,300+ or -800, 16,100+ or -1100, 19,100+ or -3000, 70,900+ or -1500, 93,100+ or -2600, and 105,400+ or -2200 years; a still-older, highly weathered and eroded moraine is undated, but likely is at least 165,000 years old. The moraine ages and relative extent of the Icicle Creek glacier correspond closely to the ages and relative amplitude of July insolation minima at 47.5 degrees N latitude. They also are in accord with ages for glaciations in the European Alps that were inferred by Milutin Milankovitch and colleagues in the 1920s based on calculations of summer insolation. Evidence that the greatest Late Pleistocene glacier advance occurred at the onset of the last glaciation (during marine isotope substage 5d) is consistent with a cooling climate and major glacier advances at that time elsewhere in North America and the Eurasian Arctic, with a dramatic increase in global ice volume, and with the shifting track of the jet stream over northwestern United States.