Pleistocene Glaciation in the Southern Part of the North Cascade Range, Washington

Previous Studies

Stratigraphic Usage Sediments resulting from an ice advance were collectively mapped as drift including till, erratics outwash, lacustrine sediments, and ice-contact stratified drift. Glacial-stratigraphic units have been used to designate the principle glacial and nonglacial episodes. The bulk of preserved interglacial deposits are constituted of loess, colluvium, alluvium, and landslide sediments.

Criteria Of Age 1)Those that are time dependent and permit relative ages to be assigned on the basis of a progressive change in degree of weathering, erosion, mass wasting, or extent of vegetation cover with increasing age of deposits 2) Those that are essentially independent of time and are based largely on spatial relationships or physical characteristics of the drifts

Weathering Rinds

Loess Thickness Maximum thickness of loess on Kittitas and Lakedale Drifts adjacent to the Yakima River and the lower reaches of its principle tributaries appears to vary systematically with the age of the underlying drift. The mean measurements at sites where loess is regarded as relatively thick ranges from 3.5 m on moraines and terraces of Swauk Prairie age to only 0.7 m on those of the Domerie.

Soils Soil profiles on each major drift sheet were sampled at 10 cm intervals. Subsequent laboratory determinations included grain-size analyses, pH, percentage of magnetic minerals, and moist color. Grain-size was clay-silt, pH tends to be slightly acidic (5-7), there were not significant percentages of magnetic minerals, the younger soils tend to be yellowish-brown and the older ones a reddish color.

Moraine and Terrace Relationships Both the relative spacing of moraines and their relative distance from cirques provide a crude basis for comparison of moraine succession in adjacent valleys, but direct correlations between valleys are possible by directly tracing outwash terraces that border the Yakima River and its principle tributaries upstream to moraines or groups of moraines belonging to each of the three major drift sheets.

Upper Yakima River Drainage Basin *Possible Pre-Thorp Drift Thorp Drift Kittitas Drift 1) Swauk Prairie Member 2) Indian John Member Post-Kittitas Soil Lakedale Drift 1) Bullfrog Member 2) Ronald Member 3) Domerie Member 4) Hyak Member 5) Lakedale Loess Holocene Sediments Post-Lakedale Soil

Possible Pre-Thorp Drift

Thorp Drift

Kittitas Drift

Swauk Prairie Member

Indian John Member

Post-Kittitas Soil

Lakedale Drift

Bullfrog Member

Ronald Member

Domerie Member

Hyak Member

Lakedale Loess

Holocene Sediments

Post-Lakedale Soils

Drift of the Puget Lobe

Pre-Vashon Drift

Vashon Drift

Chronology and Regional Correlations