Glacial erratic boulders of King County are large glacial erratic boulders of rock which were moved into King County, Washington by glacial action during previous ice ages.
The Pleistocene ice age glaciation of Puget Sound created many of the geographical features of the region, including Puget Sound itself,[1] and the erratics are one of the remnants of that age.[2] According to Nick Zentner of Central Washington University Department of Geological Sciences, "Canadian rocks [are] strewn all over the Puget lowland, stretching from the Olympic Peninsula clear over to the Cascade Range."[3] Erratics can be found at altitudes up to about 1,300–1,600 feet (400–490 m) in the Enumclaw area,[4] along with kames, drumlins,[5] and perhaps also the unique Mima mounds.[6] The soil of Seattle, the county's (and state's) largest city, is approximately 80% glacial drift, most of which is Vashon glacial deposits (till),[7] and nearly all of the city's major named hills are characterized as drumlins (Beacon Hill, First Hill, Capitol Hill, Queen Anne Hill) or drift uplands (Magnolia, West Seattle).[3][8] Boulders greater than 3 meters in diameter are "rare" in the Vashon till,[2] but can be found, as seen in the table below.
- ^ Troost & Booth 2008, p. 12 "During the period that the Vashon-age ice sheet covered the region, a tremendous volume of pressurized water was carried by subglacial streams and was responsible for carving the deep troughs of the modern Puget Sound."
- ^ a b Booth, Troost & Shimel 2008.
- ^ a b Geology of Seattle and the Puget Sound on YouTube, narrated by Nick Zentner (Central Washington University Department of Geological Sciences). Uploaded March 2, 2015 by Hugefloods.com (Nick Zentner and Tom Foster: Discover the Ice Age Floods).
- ^ Bretz 1913, p. 34.
- ^ Goldstein 1994.
- ^ Pailthorp, Bellamy, "Mima Mounds continue to mystify scientists", KPLU Wonders, KPLU
- ^ Troost & Booth 2008, p. 2.
- ^ Troost & Booth 2008, p. 5.