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Thurston County, Washington

If you apply for a building permit, the County checks its map to see if the project property has White Oak, Mima Mounds or the prairie soils or plants listed in the County's Critical Areas Ordinance (CAO). If it does, the entire parcel is inspected. Find details in the "Gopher & Prairie Plant Inspection" info sheet . 


Important 2023 Prairie Plant Inspection Dates 

  • Prairie Plant Inspection season is exptected to open in April, and run through mid-September. No-contact inspections continue for 2023.
  • Applications are accepted year-round, but per CAO code, the inspection window is spring to early fall. 


Basic Inspection Information  

  • Praire plant inspections start mid-April and end mid-September. (Applications are accepted and prescreened year-round). 
  • Properites are visited one or two times, depending on site conditions. Entire parcel is inspected.
  • Follow mowing requirements carefully so ground is visible. No mowing three weeks before inspection. Mowing may lead to reinspection, which could cause delays in processing your application.
  • Don’t dig, move dirt, pull stumps, add gravel or level mounds until AFTER project is permitted.
  • An inspector walks the entire property looking for prairie plants, White Oak and Mima Mounds as listed in the CAO (linked above).
  • After the site visit, the project status is updated in the online permit status lookup, and the project case manager is notified. 


General prairie criteria

  • 3 or more CAO-listed prairie plants close together (about 16 feet). Or
  • 25 individual CAO listed plants or species on the project site. Or
  • Presence of plants that provide food or shelter for the Taylors checkerspot butterfly (a federally endangered species) or other protected butterfly species. Or
  • Presence of rare plants classified as such by Washington's Natural Heritage Program.


If prairie plants are found 

Some applicants modified their plans a bit to avoid mitigation requirements. Others applied for a Reasonable Use Exception (forms & information on the Permit Applications & Forms page). Others worked with prairie plant biologists to create a mitigation plan to replace prairie plants onsite that will be lost to the building project. Staff can discuss the options with you. All applications are processed in accordance with the county’s Critical Area Ordinance


Helpful Fact Sheets, Documents & Information

Prairie Plant Manual    |     White Oak fact sheet     |    Gopher & Prairie Plant fact sheet     |    Prairie Soils & Gopher Soils list    |    Prairie Plant List in the Critical Areas Ordinance (scroll down to tables 14 and 15)    |    Critical Areas Ordinance/Title 24    |    2022 Letter to Prairie Inspectors    |
2022 Inspection Guidelines     |    2022 Inspector Report Standards  |   2022 CAO Prairie Plant Data Sheets