Glacial erratic boulders of King County, Washington

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.

Locations of glacial erratics in King County, Washington

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.

List of boulders
Name and descriptionHeightImage
Beaver Lake Preserve erratics are glacial erratics in and around protected space in Sammamish, weighing up to 100 tons.[9] The lake is a kettle lake also due to glaciation.[9] In the 1950s otters would reportedly rest on the large erratic at the north end of Beaver Lake.[10]

47°35′31.1″N 121°59′27.0″W
Big Rock is an 8-foot (2.4 m) tall glacial erratic in the city of Duvall. A Duvall road, a park, and several businesses are named after it.[11][12] The rock, and two non-native sequoias adjacent to it probably planted by area pioneers, are a local landmark.[13] The erratic lies in what is said to be the smallest King County park, 20 by 70 feet (6.1 m × 21.3 m) in extent, that barely contains the rock and sequoias.[14] The two lanes of Big Rock Road used to split into a wye around the rock, until a shopping center was built nearby in the 1990s.[14][13]

47°43.542′N 121°59.189′W

 8 feet (2.4 m)
Big Rock Park erratic is a glacial erratic in the eponymous city park in Sammamish. Sammamish considered naming the park "Bigger Rock Park" to distinguish it from the identically named park in Duvall.[15]

47.600°N 122.0469°W / 47.600; -122.0469 (Big Rock Park erratic)

 8 feet (2.4 m)
Cascadia College erratic

Saved from destruction by sit-in conducted by Cascadia College environmental politics students, and relocated away from construction site.[16][17][18][19][20] The rock, which several students occupied during the sit-in, was about 2 meters across before being jackhammered to two thirds its original size.[19]

47.76059°N 122.18886°W / 47.76059; -122.18886 (Cascadia College erratic)

 3 feet (0.91 m)
Des Moines Beach erratic near Des Moines Beach Park in Des Moines

8 by 6 by 4.5 feet (2.4 m × 1.8 m × 1.4 m)[21]

47°24.250′N 122°19.848′W

 4.5 feet (1.4 m)
Discovery Park beach erratics

Four or more erratics on beach below Discovery Park. Largest is 15.33 feet (4.67 m) high, 69.5 feet (21.2 m) in circumference.[22]

47°40.124′N 122°25.210′W

 15.33 feet (4.67 m)
Fantastic Erratic is a glacial erratic in Cougar Mountain Regional Wildland Park near Bellevue. It is approximately the size of a two-car garage, and 15 feet (4.6 m) high.[23][24]

47°31′48.9″N 122°4′49.7″W

 15 feet (4.6 m)
Four Mile Rock (also Fourmile Rock) is a round granite erratic, approximately 20 feet (6.1 m) across, in the intertidal zone below Seattle's Magnolia Bluff and 60 yards offshore.[25] It has had a navigational light placed on it and appears on nautical charts.[26]

Native Americans called the rock LE'plEpL, also written La'pub, and also called it Tele'tla (meaning "rock"). A legend says that a hero named Sta'kub could throw a giant cedar and hazel branch dragnet over the rock while standing at the beach.[27]

47°38′20″N 122°24′48″W[28]

 15 feet (4.6 m)
Unnamed erratic at Highline College. Granitic with "textbook en echelon dikes". 21 by 12 feet (6.4 m × 3.7 m) and 9 feet (2.7 m) high.[29]

47.38730°N 122.30173°W / 47.38730; -122.30173 (Highline CC)

 9 feet (2.7 m)
Homage artwork boulders, three locations in Bridle Trails neighborhood of Bellevue,[30] using "local granite boulders".[31] Exposed granitic bedrock does not occur in western King County.[32]

47°37′57.8″N 122°10′46.3″W (NE 24th)
47.6463°N 122.1644°W / 47.6463; -122.1644 ('Homage' boulders (NE 40th)) (NE 40th)
47.6605°N 122.1533°W / 47.6605; -122.1533 ('Homage' boulders (NE 60th)) (NE 60th)
Leschi Park erratic in Seattle's Leschi Park is a sandstone erratic with many embedded bivalve fossils. Analysis of the fossils and the rock's minerals shows it may have come from the Nooksack Group near Mount Baker, or from the Harrison Lake area of southern British Columbia.[33]

47.60103°N 122.28897°W / 47.60103; -122.28897 (Leschi Park erratic)

 5 feet (1.5 m)
Lone Rock in Tiger Mountain State Forest on Tiger Mountain[34][35]

47°29.94′N 121°58.17′W

 c. 15 feet (4.6 m)
Ravenna Park erratic in Ravenna Park in Seattle, a granodiorite stone three yards (2.75 meters) tall in Ravenna Creek with a wooden footbridge that wraps around it.[36][37]

47.67183°N 122.30689°W / 47.67183; -122.30689 (Ravenna Park erratic)

 c. 10 feet (3.0 m)
Talus Rocks, a collection of piled erratics in Tiger Mountain State Forest on Tiger Mountain,[38][39][40] forming rock caves (called "Devil's Dens" in New England[41]) said to be among the largest in Washington.[42]

47°31′07.1″N 121°59′49.2″W

 c. 12 feet (3.7 m)
Thornton Creek erratic near 17th Ave. NE and NE 104th St., in Seattle Parks' Kingfisher Natural Area. A local conservation group calls the area containing the boulder "Erratic Flats".[43]

47°42′14″N 122°18′37″W

 c. 8 feet (2.4 m)
Wedgwood Rock is a glacial erratic (and known to geologists as the "Wedgwood Erratic") near the neighborhood of Wedgwood in Seattle, Washington. It is 80 feet (24 m) in circumference and 19 feet (5.8 m) or 26 feet (8 m)[44] in height. Since 1970 it has been an offense punishable by a $100 fine to climb the rock.[45]

47.68084°N 122.2973°W / 47.68084; -122.2973 (Wedgwood Rock)

 26 feet (8 m)
Anonymous erratic in Wedgwood Square Park[46]

47.6882°N 122.2948°W / 47.6882; -122.2948 (Wedgwood Square erratic)

 c. 4 feet (1.2 m)

References
Notes
  1. 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."
  2. Booth, Troost & Shimel 2008.
  3. 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).
  4. Bretz 1913, p. 34.
  5. Goldstein 1994.
  6. Pailthorp, Bellamy, "Mima Mounds continue to mystify scientists", KPLU Wonders, KPLU
  7. Troost & Booth 2008, p. 2.
  8. Troost & Booth 2008, p. 5.
  9. D. Bruce Morgan, Beaver Lake Geology, Sammamish, Washington: Beaver Lake Community Club
  10. Morgan 2012, p. 1.
  11. Dave Tucker (April 12, 2011), Dave Tucker (ed.), "'Big Rock' (another one) in Duvall, Washington", Northwest Geology Field Trips
  12. Duvall Visitors Guide (PDF), Duvall Chamber of Commerce, 2015
  13. Louis T. Corsaletti (March 10, 1998), "Big Rock, Big Trees, Little Park -- New Safeway Being Built Near Tiny Duvall Landmark", The Seattle Times
  14. "Washington Rock is County Park", Reading Eagle, Reading, Pennsylvania, p. 42, May 15, 1977
  15. "Lame names | Sammamish can't find permanent title for SE 8th Street Park". 28 February 2013.
  16. "Cascadia Community College students move into action to save a piece of geologic history", Bothell/Kenmore Reporter, February 22, 2010
  17. "Cascadia students save Ice Age boulder, get it moved from construction site | Bothell | Seattle News, Weather, Sports, Breaking News | KOMO News". Archived from the original on 2015-04-17. Retrieved 2015-04-08.
  18. Students Sit In to Save Boulder at Cascadia (Press release), Cascadia Community College, February 12, 2010, archived from the original on 2010-05-27
  19. Kristi O'Harran (February 23, 2010), "Cascadia College rock-solid about its boulder", Everett Herald
  20. Micah Silke (September 26, 2012), "Construction: UWB 3 and the Sports and Recreation Complex", Husky Herald, University of Washington at Bothell, archived from the original on September 24, 2015
  21. Bud Hardwick (c. 2011), Dave Tucker (ed.), "Des Moines Beach erratic", Northwest Geology Field Trips
  22. "Beach Erratics at Discovery Park, Seattle". 27 January 2012.
  23. Greg Kulseth (June 30, 2011), Dave Tucker (ed.), "Fantastic Erratic, Cougar Mountain Regional Park, King County", Northwest Geology Field Trips
  24. Stekel 2009, p. 152.
  25. Ray 1891, p. 37.
  26. Puget Sound – Shilshole Bay to Commencement Bay (PDF) (Natucial chart), National Oceanic and Atmospheric Administration National Ocean Service, Office of Coast Survey, 2015, NOAA Chart 18474, archived from the original (PDF) on 2015-04-27, retrieved 2015-04-03
  27. Waterman 1922, p. 188.
  28. U.S. Geological Survey Geographic Names Information System: Fourmile Rock
  29. Magmatist (February 21, 2012), Dave Tucker (ed.), "Thin en echelon dikes in the Highline Community College erratic", Northwest Geology Field Trips
  30. Bridle Trails art, City of Bellevue Department of Planning & Community Development, 2014
  31. Bruce Myers, Bridle Trials Artist's Statement (Homage) (PDF), City of Bellevue Arts Program
  32. Livingston 1971, p. 31 Figure 12, "Relation of metallic ore deposits to granitic rocks in King County, Washington"
  33. Dave Tucker; Doug McKeever; Wes Gannaway (2011), Dave Tucker (ed.), "The fossil-rich erratic at Leschi Park", Northwest Geology Field Trips
  34. Alan Gibbs, Tiger Mountain Trail north, Washington Trails Association
  35. Jon F. Stanley (November 1, 2008), Tiger Mountain State Forest trail map (PDF), switchbacks.com
  36. Hutton 2012.
  37. Dave Tucker (May 6, 2011), Dave Tucker (ed.), "Ravenna Park granodiorite erratic, Seattle", Northwest Geology Field Trips
  38. Weber & Stevens 2010, p. 101.
  39. Dolan 2004, p. 167.
  40. Talus Rock trail, Washington Trails Association, retrieved 2015-04-20
  41. Daniel V. Boudillion (2009), "Picture Glossary of New England Lithic Constructions", New England megaliths field journal
  42. West Tiger Mountain NRCA, Washington State Department of Natural Resources, archived from the original on 2013-04-17, retrieved 2015-04-20
  43. Kingfisher Forest Stewards (November 2, 2014), Kingfisher Natural Area events, Green Seattle Partnerships
  44. Troost & Booth 2008.
  45. David Wilma (July 24, 2001), "Seattle Neighborhoods: Wedgwood -- Thumbnail History", HistoryLink, Seattle: History Ink
  46. http://wedgwoodinseattlehistory.com/2012/03/15/parks-in-wedgwood/
Sources

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