How do geologists think about a watershed?

Rivers are just the surface

WATER &

SEDIMENTS!

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

Yakima watershed underpinnings

crystalline metamorphic rocks & granites--not very permeable

mostly sedimentary rocks--generally permeableexcept clays

basalts--permeable alongfaults

Adapted from Field Trip Guidebook to the Natural History of Kittitas County – J. Mabry

NW SE

before 200 million years

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)

play animations

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

Land gradually added to west coast since 200 million years ago

added land

Land soon to be scraped off onto the continent

terrestrial sedimentation and swamps 65-35 million years ago

Future Yakima Watershed(river sediments and swamp muck with a few basalt flows thrown in)

Columbia FloodBasalts

massive basalt flows 17-14 million yr

a single flow

Photo compliments of Nick Zenter

N-S compression gently folds

Yakima watershed

15 million years to present

Wells and Simpson (2001)

ridges

agriculturalvalleys

Ice Age - last 2 million

former glaciers’ paths

Yakima watershed underpinnings

crystalline metamorphic rocks & granites--not very permeable

mostly sedimentary rocks--generally permeableexcept clays

basalts--permeable alongfaults

Adapted from Field Trip Guidebook to the Natural History of Kittitas County – J. Mabry

NW SE

From Jones et al., 2006 (USGS)

From Fuhrer et al., 2004 (USGS)