Geology of Tamanowas Rock and Peregrine’s Rock, Chimacum, WA
On Saturday, July 8th, QGS geologists will lead a 4-mile, 4-hour hike from HJ Carroll County Park near Chimacum to the Tamanowas Rock Sanctuary, then up on top of Tamanowas Ridge to see Peregrine’s Rock. This is a repeat of our well attended trip in July 2022.
This 4-mile hike is is a moderate slow-paced walk tailored to agile citizen scientists who are already knowledgeable about geologic principles and vocabulary.
Subjects discussed on the field trip include the glacial history of the Quimper Peninsula (specifically Chimacum Valley), glacial erratics on the Peninsula, and the geology of the underlying Eocene volcanic rocks that form Tamanowas Rock. This feature is a special part of the story and a sacred place of the S’Kallum people.
Tamanowas Rock is the remnant of an explosive volcano that erupted about 43 million years ago. It is comprised of adakite, an unusual type of lava that forms under anomalously high temperatures when a subducted oceanic plate starts to melt.
Conversely, Peregrine Rock is a glacial erratic named by Eric Nagle, a participant in our Great Erratic Challenge three years ago. It currently is the largest erratic we have found on the Quimper Peninsula (see Great Erratic Challenge under Resources in the menu bar).
Registration for the field trip will start June 14th (Wednesday) and close on June 28th (Wednesday). The limit is 40 participants, but we will keep a short waitlist for any cancellations. The registration form will be posted here for download. The cost is $20/person and a detailed field trip guide may be found on the Field Trip tab/ Regional Field Trips subtab in the menu bar (copies will not be provided the day of the trip).
Calcrete is a CaCO3-rich hardpan paleosol that forms in dry, stable landscapes of the world. Calcrete in eastern Washington cements a 20-m-thick interval across three geomorphic domains: Palouse Hills, Channeled Scablands, and Yakima Fold Belt. The sheet-like calcrete deposit encloses ancient Scabland flood gravels and defines a regional paleosurface that has been bent and broken by Quaternary faults. Calcrete overprints primarily lowland alluvial deposits (ancestral Columbia-Snake River floodplain) and basaltic alluvial fan gravels shed from fault-bounded ridges. Thick layers of pedogenic carbonate accumulated during the Pleistocene, between about 1.8 million years ago to about 40 thousand years ago, but older cements at somewhat deeper levels date back to ~7 million years (late Miocene). The appearance of arid-land calcrete ineastern Washington coincides with the topographic rise of the Cascade Range and establishment of a strong rain shadow east of the divide. This study sheds new light on this lesser-known part of eastern Washington’s stratigraphy.
The Speaker