Willamette Valley

The Willamette Valley is a large, fertile plain in Oregon. It sits in the Pacific Northwest region of the United States.

This valley serves as the cultural and political heart of the state. It is home to approximately 70 percent of Oregon's total population. The valley contains the five largest cities in Oregon: Portland, Eugene, Salem, Gresham, and Hillsboro. It is defined by a broad plain surrounded by mountains on three sides. The Cascade Range sits to the east. The Oregon Coast Range lies to the west. The Calapooya Mountains form the southern boundary.

The geography of the valley is shaped by the Willamette River. This river flows the entire length of the valley. The river and its many tributaries are vital to the local economy. They deposit highly fertile alluvial soils across the flat plain. These soils are the result of massive geological events. During the last ice age, enormous floods occurred. These floods came from the rupturing of an ice dam at Lake Missoula in Montana. The water swept across Eastern Washington and into the Columbia River Gorge. When the water hit log and ice jams at Kalama, it backed up. This caused the entire Willamette Valley to fill with water. Geologists call this massive body of water Lake Allison.

As Lake Allison gradually drained, it left behind thick layers of sedimentary soil. These layers reach a height of about 30 feet above current sea level. This process created the deep, rich soil found in the Tualatin, Yamhill, and Willamette valleys. Geologist Ira S. Allison first described this specific "Willamette Silt" soil in 1953. He noted its similarities to soils found in Eastern Washington. The floods also moved massive boulders called erratics. These rocks were carried on icebergs and deposited around the valley hills. One famous example is the Bellevue Erratic near McMinnville. Even the Willamette Meteorite is believed to have been moved here by these ancient floods.

The climate of the valley is a mix of two different systems. It has Mediterranean and oceanic influences. The Köppen climate classification system labels it as Mediterranean. However, it is cooler and wetter than a typical Mediterranean climate. Winters are consistently wet, cloudy, and often foggy.

Despite the clouds, winters are mild. Daytime temperatures almost always rise above freezing. Snow is rare and usually very light. Summers are quite different from the wet winters. The North Pacific High brings warm, sunny afternoons and little humidity.

Nights usually remain cool and provide relief from the daytime heat.

Agriculture is a massive part of life in the Willamette Valley. The fertile soil supports over 170 different types of crops and livestock. The valley produces most of the Christmas trees and hazelnuts sold in North America. It is also a major source of cool-season forage and turf grass. Farmers here grow wheat, oats, mint, and hops.

The valley is also famous for the marionberry. This berry was bred at Oregon State University. It is a cross between Chehalem and Olallie blackberries. It was named after Marion County, where most field trials occurred. The berry is known for a tart-yet-sweet flavor.

In recent decades, the valley has become famous for its wine. It is often called "Oregon Wine Country." There are more than 500 wineries located throughout the region.

The valley's cool, moist climate is perfect for certain grapes. It is home to some of the best Pinot noir and Pinot gris in the world. Many vineyards are located on the leeward slopes of the Coast Range. Yamhill County contains the largest concentration of these wineries. Some experts even divide the valley into northern and southern wine regions. They use the latitude of Salem as the dividing line.

The landscape of the valley has changed significantly over time. Historically, the area was mostly an oak savanna. This consisted of tall grasslands with scattered Garry oaks and Douglas-fir groves. Native American inhabitants maintained this landscape by using frequent fires. These fires encouraged the open grasslands and prevented too many young trees from growing. Since the 19th century, American settlers have suppressed these fires. They converted much of the natural grassland into agricultural fields. This change has significantly altered the original ecology of the valley floor.