Several Hydrophiles joined with Roy Haggerty's GEO 487 class to learn about the Hydrogeologic Units of the Willamette Valley on a cloudy, but not rainy, day last May. Roy was the trip leader and took us around to outcrops of most of the aquifers in the valley, starting with the deepest and ending at the shallowest.

First aquifer -- Basement Confining Unit.

The first stop was at the Coffin Butte Quarry to see the oldest and deepest hydrogeolgic unit. This unit consists of the Siletz River Volcanics. These basalts originated as submarine volcanics during the Eocene. The unit is characterized by lots of fractures, and well yields usually are only around a few gallons per min.
	Also a part of the BCU is the Spencer Formation, which outcrops near Helmick State Park. This unit is formed of Eocene sedimentary rocks, eg.consolidated shales, mudstones, siltstones, sandstones, and turbidites.

Second Aquifer -- Columbia River Basalts Lying on top of the Basement Unit are the Columbia River Basalts, which are exquisitely exampled at Silver Falls State Park. This unit consists of lava flows that originated near the present-day Oregon/Idaho border during the Miocene. The highest permeabilities are located in the cracks between the successive lava flows (known as the interflow zones). The main body of the flows have very low permeabilities, which makes this unit very anisotropic.

	Third Aquifer -- Linn Gravels/Willamette Aquifer Our next stop was an excavation pit owned by Walling Sand & Gravel, which shows the coarse-grained Willamette Aquifer. This unit consists of Basin-Fill sediments from the Coast Range and Cascades rivers.
This unit is not entirely gravels, as Roy shows off a sand lens at the Walling pit.

Fourth Aquifer -- Willamette Silts Our last stop was the east bank of Irish Bend on the Willamette River, which shows us the fine-grained Willamette Silts layer. These silts were brought into the valley during the Missoula Floods (about 15-12,000 yrs ago). This unit has very low permeabilities, and is not used much as an aquifer, but it does act as an aquitard to the Willamette Aquifer below.

After the trip was done, several of the Hydrophiles and Roy's students convened at Roy's house for dinner.