Watershed LocationThe Yamhill Watershed is located within five counties, including Yamhill, Lincoln, Polk, Washington and a bit of Tillamook. The Yamhill River flows East from the Coast Range and eventually runs into the Willamette River. The Yamhill River begins in Grande Ronde then passes through towns such as Sheridan and McMinnville.

General Geology

There is a diverse amount of geology in Oregon. The majority of bedrock in the drainage is Basalt, which creates some dynamic headwater streams. The lower elevations of most northwest Oregon streams, including the Yamhill Drainage, are composed of sedimentary rock in the floodplains. Detailed information about the bedrock of Oregon can be found through USGS.

Hydrologic Summary

The large amount of streams in the drainage can be viewed in figures 1 & 5. As in most river systems in Oregon, there is an abundance of tributaries, especially in the headwaters, where streams quickly develop due to large amounts of precipitation and come together to form the two major forks (North and South Fork) to the Yamhill. The lower, meandering section has relatively few tributaries as it winds its way to the confluence with the Willamette.

Conclusions

The Yamhill Watershed is comprised of many different ecosystems, bedrocks, soils and vegetation types. like all great rivers the Yamhill ‘is sure to get where it is going and doesn’t want to go anywhere else”. ~ Hal Boyle

References CitedGoogle Imageswww.google.com/imagesGeology Map of OregonGeorge Walder and Norman MacLeod. USGS.Dept. of Agriculture. "Natural Resources Data Department." Http://www.oregon.gov/DAS/EISPD/GEO/index.shtmUniversity of Oregon: Geographic information Systemshttp://libweb.uoregon.edu/map/map_section/quad_list.htmUSGS website - www.usgs.govProfessor Taylor’s website - www.wou.edu/taylors

Yamhill WatershedPrepared by:

Aquilegia Leet and Jacob CruserEarth Science 341

Figure 2: The Yamhill watershed is shown here in the northwest portion of Oregon.

Physiology

The Yamhill Drainage ranges from steep tributaries coming out of the coast range to the meandering sections of the lower portion through the farmlands and floodplains. The upper, high gradient sections are short lived as this is an old drainage that has long been eroding the surrounding hills. Bedrock can be encountered in the streams, but it is not as common as those rivers coming out of the Cascades. The vegetation coverage is lush due to high amounts of precipitation and abundant sources of nutrients from the surrounding hills and floodplains. Both the extensive stream network and vegetation diversity can be viewed in figure 1.

Figure 3: Yamhill Drainage digital orthographic quadrangles.

Lower Yamhill River.

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Figure 4: 7.5’ quadrangles the Yamhill Drainage encompasses.

Land use

In the Yamhill drainage 89% of the land is privately owned, while the remaining 11% is Federally owned. Much of the privately owned land is used for farming and the forestry Industry. The top three crops produced on these lands are grass seeds, wheat and Christmas trees. A portion of the land in the surrounding counties has been set aside for the Grande Ronde reservation.

Figure 9: DOQ (Digital Orthophoto Quad’s)

Figure 5: Yamhill streams overlaying a model of annual precipitation in the area.

345 N. Monmouth Ave. Monmouth, OR 97631

Figure 1: Streams over vegetation

Figure 6: A digital elevation model of the Yamhill Drainage

Figure 7: Geology Figure 8: Roads and Highways

Figure 9: Wetlands. Figure 10: Soils

Roads in the area consist mostly of rural roads leading to homes, along with a plethora of logging roads networking the surrounding hills. The main highways bisecting the area are HWYS 18 & 22.

This is a detailed view of the difference between the lower elevation rocks and higher, Coastal Range rocks. In the basin we have lacustrian and fluvial sedimentary rocks from the Pleistocene and Holocene ages. The mountains are built from volcanics of the Eocene age.

The abundant rainfall in western Oregon creates a large network of wetlands in the drainage. The presence of wetlands creates biodiversity, and biodiversity increases the health of the ecosystem.

The soils of the Yamhill watershed vary greatly, from young sedimentary soils along the river bed to very well developed soils on the mountain slopes.