South Prairie Lake

South Prairie is a seasonal lake located within Gifford Pinchot National Forest in Washington, United States.[1] For most of the year, South Prairie is a dry meadow, but every spring, it becomes an 85-acre lake.[2] Specific mechanisms that cause the seasonal inundation of the meadow are not clearly understood. It is possible that ice accumulation in the adjacent Big Lava Bed prevents drainage until weather warms sufficiently to melt the ice.[3]

A small grove of quaking aspen exists at the edge of the coniferous forested area that is annually inundated. Large-diameter black cottonwoods are found within the meadow itself; these cottonwoods stand in the middle of the lake when the meadow is flooded.[4]

South Prairie is home to the largest known population of pale blue-eyed grass, Sisyrinchium sarmentosum, a rare species of iris that was first discovered here in 1893.[5] South Prairie is the type locality, and hosts the largest and most genetically variable known population of the species.[6]

References

 This article incorporates public domain material from Jessica L. Hudec, Jessica E. Halofsky, David L. Peterson, and Joanne J. Ho. Climate Change Vulnerability and Adaptation in Southwest Washington (PDF). United States Forest Service. Retrieved 2025-06-07.{{citation}}: CS1 maint: multiple names: authors list (link)

  1. ^ "South Prairie Lake". Geographic Names Information System. United States Geological Survey, United States Department of the Interior. Retrieved June 22, 2025.
  2. ^ https://wa100.dnr.wa.gov/south-cascades/south-prairie-lake
  3. ^ Climate Change Vulnerability and Adaptation in Southwest Washington p. 155
  4. ^ Climate Change Vulnerability and Adaptation in Southwest Washington p. 155
  5. ^ https://www.opb.org/television/programs/oregon-field-guide/article/disappearing-lake/
  6. ^ Ruchty, A. 2011. Conservation strategy for Sisyrinchium sarmentosum Suks. ex Green. Portland, OR: U.S. Department of Agriculture, Forest Service and U.S. Department of the Interior, Bureau of Land Management

45°54′46″N 121°41′49″W / 45.91278°N 121.69694°W / 45.91278; -121.69694


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