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Terrestrial
Projects:
Point Defiance
Park geology |
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Introduction to the geology of Point Defiance
Park
In examining the
stratigraphy along the shoreline of Point Defiance, there are three main visible
layers. The bottom, or oldest, layer is comprised of the “Defiance Clays.”
This is followed by a layer of unnamed silts, sands, and gravels. The top, or
youngest, layer visible along the shoreline is comprised of Colvos sand. All of
the layers are discontinuous “largely due to topographic variations at the time
of their deposition.”
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View
Map |
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Approximate Age |
Name |
Source
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Additional Information |
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15000-17000 years |
Colvos Sand |
“outwash deposits laid down [ahead] of the advancing
ice sheet during the most recent glacial advance (Fraser
Glaciation).” |
In some areas, clays or
silts observed in base, likely former lake deposits.
Observed cross bedding
supports the movement of sediment by streams or rivers.
The Colvos Sand is
thought to be correlative to the Esperance Sand, which is commonly exposed
in the Puget Sound lowlands
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Uncertain |
Unnamed silts, sands,
and gravels |
“likely deposited by
rivers during the Olympia interglacial (between the 2 most recent ice
advances)” |
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> 46,000 years |
Defiance clay
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Lake deposits, lake
likely created ahead of an older glacier advancing S from Canadian Rockies. |
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(Information provided by
Dr. Michael Valentine, Geology Dept., University of Puget Sound)
Webpage and project content by:
Dr. Joel Elliott, University of Puget
Sound, Department of Biology
Liz Fly, University of Puget Sound, Department of Biology
Erin Spear, University of Puget Sound, Department of Biology
This project is funded by the
Northwest Academic Computing Consortium and the University of Puget
Sound .
jkelliott@ups.edu |
lfly@ups.edu | Send Feedback!
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