South Yamhill River
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The South Yamhill River is a tributary of the Yamhill River, approximately 50 mi (80 km) long, in northwest Oregon in the United States. It drains an area of the Coast Range, as well as part of the Willamette Valley west of the Willamette River.
It rises in the Siuslaw National Forest in the Coast Range along the county line between Tillamook and Yamhill counties, near the Grand Ronde Indian Reservation. It flows SSE, then generally ENE, through the Van Duzer State Forest, past Grand Ronde and Sheridan, then northwest, joining the North Yamhill River from the south approximately 2 mi (3.2 km) east of McMinnville to form the Yamhill.
In its upper reaches in the mountains it flows through timber-producing forests, broadening into an agricultural valley and emerging into the larger Willamette Valley near Sheridan. The valley of the river is especially fertile, with many orchards and berry farms.
The river valley is essentially a break in the line of higher mountains in the Coastal Range, located in a region of gentle hills between the coast and the Willamette Valley. The valley provides the route of Oregon Route 18, one of the most popular routes to the Oregon Coast from Portland and the population centers of the northern Willamette Valley.
The South Yamnill river levels are measured by the National Weather Service at two locations:
- Near Willamina (river code WLAO3) located in Polk County at an elevation of 236 feet (Latitude: 45 2' 49" Longitude: 123 30' 10")
- At McMinnville (river code MCMO3) located in Yamhill County at an elevation of 62 feet (Latitude: 45 12' 21" Longitude: 123 10' 52")
The McMinnville river gauge has been gathering data since 1994. The highest river level measured during that period was 41.26 feet in 1997 and the lowest was 14.58 feet in 2001.
The Willamina river gauge has been gathering data since 1934. The highest river level measured during that period was 8.43 1947 feet and the lowest was 1.05 feet in 1977.
