Oregon’s culinary Superabundance is rooted in soils that formed over billions of years

By Heather Arndt Anderson (OPB)
Feb. 24, 2023 1 p.m.

From the lava plains of the Alvord Desert to the fertile alluvium of the Willamette Valley, Oregon’s secret wealth is lying all around us. It’s an ingredient forged from stars, fire and ice and, though often overlooked, is key to the state’s food systems. It’s soil.

Of the 12 soil orders of the world, Oregon has all but two: gelisols (permafrost soils in the tundra) and oxisols (those found in tropical rainforests). That’s right: More than 80% of the world’s soil types are found in Oregon.

Outline of Oregon showing that most of the state was under the ocean 200 million years ago.

Most of what is now Oregon was under water 200 million years ago.

MacGregor Campbell / OPB

To understand how that came to be, you’ll need to pan out.

A few billion years after planet Earth formed, the supercontinent Pangea slowly began breaking apart. The smaller continents that resulted spent billions of years shifting around, converging, diverging and crashing into each other.

Related: Superabundant dispatch: Digging into Oregon’s filthiest riches — our soils

Sediments from the bottom of the sea gradually made their way upward and out of the water. These marine deposits are still found throughout the highest mountain ranges in western North America. This adds calcium to soils, which improves soil structure by binding organic matter to clay particles, and it’s a mineral that plants need for their cell walls. Blossom end rot in tomatoes is often linked to calcium deficiency, and crucifers like broccoli and kale need lots of it.

Columbia River basalt

The earth’s crust is still moving (albeit slowly), but sometimes much faster geologic events form new soil.

A map of Columbia River Basalt Group highlighting the Steens Mountain and Picture Gorge sub-units and areas where Oregon sunstones have been found.

A map of Columbia River Basalt Group.


In northern and eastern Oregon, in a series of events known as the Columbia River Basalt Group, lava repeatedly flowed out of cracks in the earth’s crust. It eventually subsided into a vast lava plain — the Columbia Plateau. This basalt forms the parent material across the Northwest, and over time it weathers and becomes soil. Some of the most productive grasslands, pastures, and wheat fields grow in weathered basalt. In the Northwest’s humid climate, these weathered basalt soils are also rich in the oxidized iron that helps fruit trees produce larger, juicier fruit.

Flood after flood

Later, a series of cataclysmic floods brought fertile soils to Oregon.

At the end of the ice age, 15,000 to 20,000 years ago, a massive ice dam blocking the Clark Fork of the Columbia River broke loose, sending more water gushing down the Columbia than the Great Lakes hold today.

A map showing the extent of the floods at the end of the last ice age.

About 20,000 years ago, massive amounts of water flowed through the Columbia Basin intermittently for thousands of years.

MacGregor Campbell / OPB

The ice dam reformed, new lakes formed as water impounded, and the ice dam broke again. Rinse and repeat dozens of times over 2,000 years.

These floods are now known by many names: the Missoula floods, the Bretz floods or Spokane floods. They scoured out new lakes, like eastern Oregon’s Lake Condon, and floated glaciers carrying boulders up to 36 feet in diameter.

The floods also carried gravel, sand and fertile silts and sediments from Montana, Idaho, and eastern Washington and repeatedly deposited them into the Willamette Valley.


A volcanic legacy

After floods deposited all that soil into western Oregon, a new layer of geologic inputs would arrive to alter the region’s soil: tephra — the rocks, ash and clumps of lava that fly through the air during a volcanic eruption.

a giant plume of ash blasted out of the top of an erupting Mount St. Helens volcano.

Aerial view of the May 18, 1980, eruption of Mount St. Helens as seen from the southwest. Volcanic eruptions alter the surrounding soil with deposits that gradually release magnesium and potassium, vital for plant growth.

Courtesy of the U.S. Geological Survey

Most of the many volcanoes across Oregon are no longer active, but the multiple stratovolcanoes studding the Northwest — the Cascades — aren’t all so dormant. And their eruptions have altered the soil for millennia.

The biggest bang by far came from Mount Mazama around 7,700 years ago. Mazama erupted and collapsed in on itself, leaving behind a deep hole — Crater Lake.

Ash from the explosion landed everywhere from Edmonton, Alberta, to Las Vegas, Nevada, and as far east as Yellowstone in Wyoming, leaving deposits nearly three feet deep close to the blast zone.

As it weathers over time, volcanic material releases magnesium and potassium, two elements vital for plant growth.

Mazama’s eruption spread a layer of fertilizer across the Northwest, ready to be taken up by all manner of plants and fungi.

Reddish soil.

Jory soil in a vineyard in the Willamette Valley.

Brandon Swanson / OPB

Organic inputs

Spewing volcanoes and cataclysmic floods are all well and good, but soil’s microbiome is built on organic matter — the stuff that is born, grows, reproduces, poops and dies in and on the soil. But how does dead rock become living soil?

The earliest terrestrial organisms on the planet were likely soil microbes, creating the first layers of biomass that enabled the evolution of plants. They help weather rock into soil, and then alter the soil’s chemistry. Sometimes these microorganisms become the rock again, just to be weathered back into soil again.

By changing the soil, microorganisms like bacteria and fungi have altered all life on the planet. It can be challenging to identify fossil records of microbes, but fungi are just robust enough to leave behind a record; in fact, the oldest land fossil is of a soil fungus called Tortotubus.

And earth’s largest terrestrial organism is another fungus found in the soil of eastern Oregon’s Blue Mountains: a honey fungus (Armillaria ostoyae) that spans 2,384 acres. That’s roughly 1,800 football fields, or the size of Cottage Grove.

For only a few weeks in the fall, the fungus grows visible fruit. It's from these golden caps where the honey mushroom gets its name.

The largest and possibly the oldest living organism in the world lives in Oregon's soil. It's from these golden caps that the honey mushroom gets its name.

Nick Fisher / OPB

Long story short: because Oregon’s soils are overall volcanic, they’re also acidic. Because they’re acidic, they’re fungal. And because they’re fungal, they’re more productive.

Productive soil makes a great home to everything from moles and voles to the rare Willamette giant earthworm — but it also grows better food.

Soil: more than the sum of its parts

Soils are dynamic — the ultimate interface between vegetable and fungus, animal and mineral; of the macro, and the micro. Soil is an entire cosmos, a whole world as complex and mysterious as the deepest sea, the secrets of which are waiting to be unlocked.

Soil doesn’t just affect how much food we can produce, or what we can grow — it can even affect the precise way our food tastes. And as much as it is a state of hops, berries and wine grapes, Oregon is a soil state, home to some of the most diverse soils in the world.


Tags: Science & Environment, Superabundant, Food