<
p id="
p-1">The Puget Lowland and San Juan Islands, lying in the Puget Trough between the Cascade Range and the Olym
pic Mountains, were in the
path of Pleistocene ice sheets which flowed southward from Canada.
p><
p id="
p-2">Flood
plain, silt, sand, and
peat of the Whidbey Formation were de
posited
prior to 40,000 years ago, during an interglaciation believed to be equivalent to the Puyallu
p and Sangamon Interglaciations. Possession Drift, which overlies sediments of the Whidbey Formation, is radiocarbon dated at 34,000
![]()
phic" alt="Gra
phic" src="2273/embed/inline-gra
phic-1.gif" /> years B.P. in its u
pper
part and is limited by a radiocarbon age of >39,900 in its lower
part. The Possession is correlated with late
phases of the Zyriansk Glaciation in Russia and the early Würm in Euro
pe.
p><
p id="
p-3">Peat lying on Possession Drift yielded radio-carbon dates between 27,200
![]()
phic" alt="Gra
phic" src="2273/embed/inline-gra
phic-2.gif" /> and 22,700 ± 550, re
presenting the Olym
pia Interglaciation which is correlated with the Karginsk Interglaciation of Russia, the Paudorf Interval of Euro
pe and the Farmdalian of the midwestern United States.
p><
p id="
p-4">Es
pe
rance Sand, de
posited by meltwater streams in front of advancing ice during the Fraser Glaciation and subsequently overridden during the Vashon Stade, was radiocarbon dated at 18,000 ± 400 years. During deglaciation, the ice sheet thinned until it floated in marine water and
poorly sorted, fossiliferous glaciomarine drift was de
posited in the Everson Interstade. Shell-bearing sediment at altitudes u
p to 400 feet above
present sea level and unfossiliferous glaciomarine drift u
p to 600 feet indicate that relative sea level at that time was 500 to 700 feet higher. Eighteen radio-carbon dates from marine shells in Everson glaciomarine drift vary from 10,370 ± 300 to 13,010 ± 170 years. The Everson Interstade ended with lowering of relative sea level to a
pproximately its
present
position and the disa
ppea
rance of floating ice. The following Sumas Stade ended shortly before 9,920 ± 760 years ago.
p>