Newsletter Archives > Viticulture

In the Vineyard : Fall 2005

The Dirt on Dirt,

or getting below the surface of the new AVAs

By Michael Davies, Chehalem Assistant Winemaker and Vineyard Manager, and Harry Peterson-Nedry

Great wine is grown not made, and the soil is where it begins.

Soils are dynamic and complex ecosystems that nourish plants, provide immense buffering capacities nutritionally, and in their ability to create uniqueness in what they grow, represent some of our most precious resources. Soils should and do reflect their varied histories in terms of parent material, organic matter components and climatic conditions. And, this makes all the difference between wines from one region to another, even sites within sight of each other.

Geological origins of Northern Willamette Valley Vineyard Soils
Geological origins of
Northern Willamette Valley Vineyard Soils
graphic courtesy Ray Wells, USGS

There are more than 800 distinct soil types in Oregon with approximately 60 of them where vineyards have been planted (e.g., 41 in the Chehalem Mountains AVA alone). These soils have been defined according to their origin, texture, degree of weathering, innate structure and porosity, level of organic matter, permeability and drainage properties, soil depth, available water, pH, and potential fertility. With the recent importance to the wine industry of heretofore little-valued hillside soils, reclassification and mapping projects by federal agencies (USDA and USGS) have been reprioritized since 2000, resulting in new understanding and naming for soils in our region. New maps of Northern Willamette Valley regions will be reissued within the next two years.

The geological origins of our vineyard soils determine complex, but significant differences in wines’ aromas, flavors, structure and ageability, assuming mature vineyards where roots have had the time to investigate the parent rock.

The soils spectrum we see in Oregon soils reflects the history of this part of the planet geologically, spanning 60 million years:

from the beginnings of plate activity on the west coast, literally building the western coastline as the Juan de Fuca plate began diving under the Continental plate;
to subsequent lava flows 15 million years ago that went down the Columbia Gorge into the sea over an infant Coast Range which had shortly before (20mya) been created by stress and stretching;
subsequent creation of valley sedimentary soils of the western AVAs (see graphic courtesy Ray Wells, USGS) by a process of ongoing tectonic tension raising the terrain out of the ocean, then tilting layers of ocean sediment to free it from the cover of Columbia River Basalt;
to present day when relatively recent activities like the Missoula Floods 15,000 years ago deposited soils from what is now Montana and Idaho onto the valley floor and, like a bathtub ring, up to 400 feet on the hillsides;
and glaciers 10,000 years ago which imported Canadian soils that were subsequently blown and pasted on the northern hillsides near Portland, the loess soils of the Chehalem Mountains.

At Chehalem in the context of our wines, the three soil series of most interest to us are:

Willakenzie: (as reflected in Ridgecrest and the Ribbon Ridge AVA) a silty clay loam, consisting of weathered siltstone and fine-grained sandstone marine sedimentary rock. New work now shows this soil series to consist of several soils, including Wellsdale on the top of Ribbon Ridge. It is moderately deep (between 20 and 40"), well-drained and is moderately weathered with subsoil horizons of increased clay content.
Jory: (Stoller and the Dundee Hills AVA) a red, silty clay loam whose parent materials are Columbia River basalts and therefore slightly younger than Willakenzie’s ocean sediment. This soil is deep (greater than 60"), well-drained and is highly weathered, with subsoil horizons of increased clay content.
Laurelwood: (Corral Creek and much of the varied Chehalem Mountains AVA) a silt loam made up of weathered wind-blown deposits of glacial silt (loess) over basalts, much younger than the other two soils. It is deep, well drained and is also moderately weathered.