Tokul soil

thumb|Tokul Soil profile The '''Tokul''' soil series are Andisol soils formed by volcanic ash and loess over a dense glacial till. The soils are found in the Puget lowland forests and western foothills of the Cascade Range, along the Puget Trough, which stretches from south of Seattle to the Canadian border. Tokul soils are the designated state soil of Washington state.<ref name="nrcs-description">{{cite web |title=Tokul - Washington State Soil |url=https://web.archive.org/web/20220523074625/https://www.nrcs.usda.gov/Internet/FSE_DOCUMENTS/stelprdb1237005.pdf |website=NRCS |publisher=USDA |access-date=16 March 2026}}</ref>

==Name== The Tokul soil series is named after Tokul Creek, a small tributary of the Snoqualmie River in eastern King County near Fall City, Washington and Snoqualmie Falls.<ref name="nrcs-description" /> The name of Tokul Creek itself is derived from the Lushootseed word ''dəxʷq̓al'', the name of a Snoqualmie village on the creek consisting of seven longhouses.<ref name="Waterman-Geography">{{Cite book |last1=Hilbert |first1=Vi |title=sdaʔdaʔ gʷəɬ dibəɬ ləšucid ʔacaciɬtalbixʷ - Puget Sound Geography |last2=Miller |first2=Jay |last3=Zahir |first3=Zalmai |publisher=Lushootseed Press |others=Original manuscript from T.T. Waterman |year=2001 |isbn=979-8750945764 |location= |pages=182–185 |language= |author-link1=Vi Hilbert}}</ref>

==Profile== The Tokul soil series has the following profile:<ref name="usda">{{cite web |title=TOKUL SERIES |url=https://soilseries.sc.egov.usda.gov/osd_docs/t/tokul.html |publisher=USDA |access-date=16 March 2026}}</ref>

*Surface layer: organic material *Subsurface layer: gravelly medial loam *Subsoil - upper: gravelly medial fine sandy loam *Subsoil - lower: gravelly sandy loam

Tokul soils have an organic surface, rich in decaying plant matter from the prevalent coniferous forest debris in the area. Below this, a dark-brown, organic rich, gravelly loam creates a fertile and well-drained layer, into which plant roots penetrate. This brown-reddish sub-layer, which extends {{convert|1-2|ft|m}} below the surface, is strongly influenced by volcanic ash and has high concentrations of manganese and iron. Lower still is the grayish, dense glacial till, which then was overlaid with volcanic ash and loess, or wind-blown sediment.<ref name="sssa">{{cite web |title=Tokul: Washington State Soil |url=https://www.soils4teachers.org/files/s4t/k12outreach/wa-state-soil-booklet.pdf |website=Soil 4 Teachers |publisher=Soil Science Society of America |access-date=16 March 2026}}</ref><ref name="WSU">{{cite web |title=The Soil That Makes Washington Oh So Evergreen |url=https://web.archive.org/web/20220523074625/https://www.nrcs.usda.gov/Internet/FSE_DOCUMENTS/stelprdb1237005.pdf |website=WSU Master Gardener Program of Thurston County |publisher=Washington State University Master Gardener Program |access-date=16 March 2026}}</ref>

The state has over {{convert|1,000,000|acre|km2}} of Tokul soils on the western side of the Cascade mountains.<ref name="teacher-guide">{{cite book |last1=Lucas |first1=M. D. |last2=Ross |first2=R. M. |last3=Swaby |first3=A. N. |title=he Teacher-Friendly Guide to the Earth Science of the Western US |date=2014 |publisher=Paleontological Research Institution |location=Ithaca, NY |page=252 |url=https://geology.teacherfriendlyguide.org/downloads/w/tfggw_8_soils_lr.pdf |access-date=16 March 2026}}</ref> Hundreds of other volcanic soils make up the rest of Washington's soils.<ref name="nrcs-description"></ref>

==Plant Habitat== Tokul soils are among the most productive in the world, supporting the state's rich coniferous forests, which are dominated by Douglas fir and western hemlock, the state tree of Washington.<ref name="wa_grown">{{cite web |title=Super Soils |url=https://www.wagrown.com/blog/farming/item/super-soils |website=Washington Grown |access-date=16 March 2026}}</ref><ref name="smithsonian">{{cite web |title=State Soils - Washington |url=https://forces.si.edu/soils/interactive/statesoils/html/State-Soils/Default.aspx?selection=Washington&tab=whatSpecial |publisher=Smithsonian National Museum of Natural History |access-date=16 March 2026}}</ref>

During wet periods, moisture builds up above the layer of dense glacial till, which can create unstable steep slopes. The soil series is threatened by displaced top soil as a result of development and agriculture due to lower humus content caused by tilling and digging.<ref>{{cite news |last1=Lovejoy |first1=Ann |title=Washington’s super state soil needs a little help |url=https://www.kitsapsun.com/story/life/2023/04/19/washingtons-super-state-soil-needs-a-little-help/70132796007/ |access-date=16 March 2026 |agency=Kitsap Sun |date=April 19, 2023}}</ref>

==Washington state soil== The Tokul soil series was selected by the Washington Society of Professional Soil Scientists as the official soil of Washington.<ref name="usda"></ref><ref name="nrcs-description"></ref> While the soil series has not yet been officially designated as the state soil by the state legislature, it is recognized by the USDA Natural Resources Conservation Service (NRCS) and many other agricultural and pedological organizations as the designated representative soil of Washington state.<ref name="usda"></ref>

Washington was the first state to recognize an Andisol, or a soil formed in volcanic ash, as the state soil.<ref name="smithsonian"></ref>

==References== {{reflist}}

Category:Pedology Category:Soil in the United States Category:Geology of Washington (state) Category:Types of soil Category:Symbols of Washington (state)