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Understanding the Yakima Watershed Geology

Explore the geological history of the Yakima watershed from ancient marine sediments to present-day river sediments, basalt flows, and more. Learn about the permeability of different rock types and the impact of past events on the landscape. Discover the intricate processes shaping the watershed over millions of years.

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Understanding the Yakima Watershed Geology

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  1. How do geologists think about a watershed?

  2. Rivers are just the surface

  3. WATER & SEDIMENTS!

  4. Geological river continuum: • From ridgetop raindrops & snowflakes • To sediment washing down slopes • To water & sediments in the “river” itself • To water deep below the surface

  5. Yakima watershed underpinnings NW SE basalts --permeable along faults crystalline metamorphic rocks & granites --not very permeable mostly sedimentary rocks --generally permeable except clays Adapted from Field Trip Guidebook to the Natural History of Kittitas County – J. Mabry

  6. before 200 million years N American coast over by Montana

  7. SUBDUCTION started ~200 million years ago marine sediments get scraped off the down-going plate and plastered onto the continent Volcanoes at the surface and granite cooling miles below the surface Future Yakima Watershed (metamorphosed ocean sediments)

  8. play animations http://emvc.geol.ucsb.edu/1_DownloadPage/Download_Page.html#GlobalTectonics

  9. Land gradually added to west coast since 200 million years ago added land Land soon to be scraped off onto the continent

  10. terrestrial sedimentation and swamps 65-35 million years ago Future Yakima Watershed (river sediments and swamp muck with a few basalt flows thrown in)

  11. Columbia Flood Basalts massive basalt flows 17-14 million yr

  12. a single flow Photo compliments of Nick Zenter

  13. N-S compression gently folds Yakima watershed15 million years to present Wells and Simpson (2001)

  14. agricultural valleys ridges

  15. Ice Age - last 2 million former glaciers’ paths

  16. Yakima watershed underpinnings NW SE basalts --permeable along faults crystalline metamorphic rocks & granites --not very permeable mostly sedimentary rocks --generally permeable except clays Adapted from Field Trip Guidebook to the Natural History of Kittitas County – J. Mabry

  17. From Jones et al., 2006 (USGS)

  18. From Fuhrer et al., 2004 (USGS)

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