ABSTRACT Climate during the Last Glacial Maximum (LGM) varied substantially across North America, strongly influencing changes in plant and animal distributions and causing variations in the timing and relative magnitude of ice expansion and recession. The Olympic Peninsula is a mountainous maritime terrain in northwestern Washington, where the climate today is most strongly influenced by Pacific weather systems. However, what about during the LGM, when ice sheets covered most of northern North America? Fossil beetle assemblages of LGM age contain species that currently inhabit riparian and lacustrine habitats in the boreal zone of Canada and Alaska, and in higher elevations in the Cascades and Rocky Mountains. They include three Olophrum species that today are unknown from the Olympic Peninsula. Olophrum consimile is especially well represented, and its occurrence today above 1000 m elevation in the Cascades of northern Washington State indicates summers during the LGM would have been at least 4 °C cooler than today. The absence of wood-boring beetles, in contrast to assemblages from deposits correlating with marine isotope stage (MIS) 3, supports an open rather than a forested landscape. The insect fossils also include an undescribed species of a blind trechine ground beetle, likely endemic to the Pacific Northwest with biogeographic affinities to Asia. Pollen and plant macrofossil evidence for a Sitka spruce and mountain hemlock parkland with similarities to the vegetation of modern southeast Alaska also supports an interpretation of a climate with summer temperatures ~4 °C cooler than today. Both the vegetation and the insects provide evidence that the climate was wet with persistent snow cover and not as dry as has been reported from the Puget Lowland to the east. Glacial geology provides evidence that during the colder climate of the LGM, mountain glaciers advanced down the western valleys of the Olympic Peninsula to the lowlands but not as far as they had extended during MIS 3. The amount of climatic cooling on the Olympic Peninsula during the LGM was less than at similar latitudes in midcontinental or eastern North America, indicating a strong modulation of climate by the Pacific Ocean.

ABSTRACT A tidal marsh at the head of Discovery Bay contains the longest record of tsunami deposits in Washington State. At least nine tsunami deposits dating back 2500 yr are preserved as fine sand layers in peaty tidal marsh deposits. Discovery Bay is a setting that amplifies tsunami waves, has an abundant sediment source, and a tidal marsh that traps and preserves tsunami deposits. The youngest deposit, bed 1, is probably from the 1700 A.D. Cascadia earthquake. Bed 2 has a newly revised age of 630–560 cal yr B.P. (1320–1390 A.D.), an age range that overlaps with the ages of tsunami deposits from Vancouver, British Columbia, and northern Oregon, as well as evidence for strong shaking in the region including submarine and sublacustrine slope failures. However, there is no geologic evidence for a late fourteenth-century earthquake or tsunami in any of the southwest Washington estuaries that record seven Cascadia earthquakes in the last 3500 yr. Discovery Bay bed 2 and similar-aged evidence in the region may represent a short rupture on the Cascadia subduction thrust, possibly centered west of the Strait of Juan de Fuca, that did not cause significant coastal subsidence. Other possible sources considered for bed 2 include a crustal fault earthquake, a tsunamigenic slope failure, or a transoceanic tsunami. Older tsunami deposits beds 3–9, which outnumber the number of Cascadia earthquakes in the last 2500 yr, are likely from a combination of Cascadia and non-Cascadia sources. Additional radiocarbon dating of beds 3–9 will improve age ranges and constrain potential sources.