Willamette Valley

Geological History of the
Willamette Valley


Until about 12 million years ago, western Oregon was on the floor of the Pacific Ocean. Before that, for 35 million years under the sea, it was slowly accumulating layers of marine sediment, the bedrock of the oldest soils in the Willamette Valley.

Starting about 15 million years ago, the pressure created along the coast by the collision of the Earth’s Pacific Plate and North American Plate gradually pushed western Oregon up out of the sea, creating the Coast Range and the intensely volcanic Cascades Mountains further inland. The Willamette Valley thus began as an ocean floor trapped between two emerging mountain ranges.

During this period of uprising, from about 15 million to 6 million years ago, rivers of lava erupting from volcanoes on the east side of the Cascades flowed down the Columbia Gorge towards the sea, covering the layers of marine sediment on the floor of the emerging Willamette Valley with layers of basalt.

The Willamette Valley continued to buckle and tilt under pressure from the ongoing coastal collisions, forming the interior hill chains that are typically tilted layers of volcanic basalt and sedimentary sandstone, such as the Dundee Hills and Eola Hills.

The next geologic activity to add to our soils was the creation of a layer of wind-blown silt (called “loess”) on the northeast facing hills west of where Portland sits today. The silts that were blown came from the valley floor, but originally they derived from the earlier basalts and sediments that had been severely weathered.

Much later, about 18,000 to 15,000 years ago, at the end of the last ice age, the melting of a glacial dam near the location of Missoula, Montana repeatedly flooded the Willamette Valley. It created a lake up to the 400-foot contour level, with only the tops of the two-tone hills sticking out, and leaving behind deep silts.

Thus, in the Willamette Valley there exists a complex series of soils with interesting and diverse origins.

Eola-Amity Hills

The name of this AVA is derived from a ridge of hills adjacent to the Willamette River. The ridge is actually composed of the Eola Hills, straddling the 45thlatitude on the southern end, and the Amity Hills on the northern spur. The proposed minimum elevation for the AVA is 200 feet.

Two of the predominant influences on the characteristics of wines from the Eola Hills are shallow soils and the Van Duzer Corridor. The soils of the Eola Hills contain volcanic basalt from ancient lava flows. The basalt is combined with a preponderance of marine sedimentary rocks and/or alluvial deposits. These soils: Nekia, Woodburn, and Steiwer are generally much shallower and rockier relative to most other Oregon AVAs.

These shallow well-drained soils tend to produce smaller grapes with greater concentration. The wines tend to be bigger, more full-bodied wines. The fruit components tend towards blackberry, black cherry, and plum contrasted with raspberry, strawberry, and cherry flavors, which may predominate in wines from deeper soils. The mineral content of the terroir is often present both on the nose and on the palate. The wines often display considerable focus and clarity of fruit. They also favor primary fruit character over spice, tending toward the darker black fruit spectrum (black cherries and blueberries).

Compared to other North Willamette Valley regions, the wines often exhibit brighter acidity and firmer structure, along with considerable longevity, due to the cooling effect of the Van Duzer Corridor. Wines from lower elevations tend to lean more toward plum and bramble fruit, showing slightly more secondary flavors such as earthy, mineral and spice/herbal tones (e.g. white pepper and dried flowers).

Grapes love the climate

Oregon’s Willamette Valley is the perfect place to grow Pinot Noir. Here, the longer hours of daylight and cooler growing conditions allow wine grapes to ripen slowly. These longer daylight hours allow the flavor to develop over a longer period. Harvest doesn’t normally occur until late September or early October.

The climate of the Willamette Valley is mild all year round. Winters are usually cool and wet. Summers are dry and warm. Heat above 90 °F (32 °C) occurs seldom – only 5 to 15 days per year. This temperate climate, combined with coastal marine breezes, makes for exceptional growing conditions within the Valley for Pinot Noir.


The 45th parallel cuts through the Willamette Valley just north of Salem. The Z’IVO estate vinyard is sitting half way between the equator and the North Pole, but so is Newfoundland. So what does that mean? Being so far north, between March 21 and September 21, they have more daylight hours than growing regions further south. On June 22 Willamette has 1.5 hours more sun than in Napa. These longer daylight hours, combined with cool growing conditions lead to a long period of flavor development at the end of the growing season. This is a key difference between cool- and warm-climate wines.


Ripening requires heat sufficient to physiologically mature grapes, but without depriving the grapes of acid, finesse, and complexity. Northern latitude plus proximity to the ocean brings moderate temperatures year round with no vine-killing cold in winter or serious frost in spring.

Ocean breezes bring cool nights that are especially important for Pinot during the ripening period. The Cascade Mountain range to the east protects us from the hot and cold extremes of the continental interior. Our winters are very mild with a mean January temperature of 42o F. Our summers are cool with July’s average temperature being 68o F.


Moderate rainfall at the right time is the second key to our cool-climate advantage. The Willamette Valley is protected from extreme coastal rainfall (80” annual) by the Coast Range. Although average annual rainfall here is 40″, most of it falls in the winter. Average rainfall in January is 7″, but only 0.5″ in July and August.

The cool Van Duzer Corridor

The Van Duzer is one doozy of a corridor. It helps provide the necessary temperature differential needed to grow good grapes. In brief, the Van Duzer Corridor provides a break in the Coast Mountain Range that allows cool ocean winds to reach the Willamette Valley, dropping temperatures dramatically, especially during late summer afternoons. These late afternoon and evening breezes help provide the cool nights that keep acids firm and are essential for optimal ripening. The temperature swings are often more than 30 degrees F.