Columbia River Basalt Group

A defining characteristic of all flood-basalt provinces is the prolonged eruption of enormous outpourings of lava from extensive fissure systems, preserved today in massive dike swarms. Three such areas fed the bulk of the CRBG eruptions: the Steens Mountain dike swarm of southeastern Oregon (the dominant source for the Steens Basalt; 15 percent of the CRBG volume), the Monument dike swarm of north-central Oregon (Picture Gorge Basalt; 1 percent), and the massive Chief Joseph dike swarm of northeastern Oregon and southeastern Washington (Imnaha, Grande Ronde, Wanapum and Saddle Mountains Basalts; 84 percent, about 175,000 cubic kilometres). Taubeneck (1970) estimated that the Chief Joseph swarm may contain as many as 21,000 dikes, and the great majority of CRBG dikes have north-northwest trends. The eruptions migrated northward with time: the Steens Basalt, the oldest formation, is restricted to southeastern Oregon, and progressively younger formations become progressively thicker to the north. The CRBG eruptions continued for more than 11 million years, from about 16.7 to 5.5 million years ago, but about 93 percent of the flood-basalt volume erupted in only about 1.1 million years (16.7 to 15.6 million years ago), a period of nearly constant eruption known as the main eruptive phase. Three flows of the Teepee Butte Member (Grande Ronde Basalt) exceeded a volume of 5,000 cubic kilometres, and perhaps as many as five flows of the Roza Member (Wanapum Basalt) have an estimated volume of 1,500 cubic kilometres from a fissure at least 180 km long. How fast such flows were emplaced is still debated: cooling models for the Roza Member are consistent with slow emplacement over years to a few decades, compositional data point to months to years, and one model suggests a typical 1,000 cubic kilometre sheet flow could be emplaced in less than six years, with injected batches of lava travelling 100 to 300 km from vent to flow front in less than 10 days. The thickest accumulation lies beneath the central Columbia Basin, where Miocene subsidence generated a basalt pile of subaerial flows more than 4 km thick.

• Three dike swarms fed the bulk of the eruptions: Steens Mountain (southeastern Oregon, 15 percent of CRBG volume), Monument (north-central Oregon, 1 percent) and Chief Joseph (northeastern Oregon and southeastern Washington, 84 percent)
• Taubeneck (1970) estimated the Chief Joseph swarm may contain as many as 21,000 dikes; most CRBG dikes trend north-northwest
• Eruptions began with the Steens Basalt in southeastern Oregon and migrated northward with time; about 93 percent of the volume erupted between 16.7 and 15.6 million years ago
• Emplacement rates are debated, from years to a few decades (Roza Member cooling models) to lava batches travelling 100 to 300 km in less than 10 days (one model)

The CRBG contains seven formations and numerous formal and informal members, and its combined stratigraphic column contains more than 350 extensive and mappable sheet flows. From oldest to youngest, the volumetrically significant or most studied formations are the Steens Basalt, Imnaha Basalt, Grande Ronde Basalt, Wanapum Basalt and Saddle Mountains Basalt; the Picture Gorge Basalt and Prineville Basalt are also formations but are more localized to north-central Oregon. The Steens Basalt was formally recognized in 2013 as the earliest formation of the CRBG, extending the province into southeastern Oregon; at Steens Mountain it is nearly 1 km thick. The Imnaha Basalt of the Rock Creek type is present in northeastern Oregon and southeastern Washington. The Grande Ronde Basalt constitutes 71 percent of the total CRBG volume. Its eruptions have been estimated at about 16 to 15.6 million years ago, an interval the USGS field guide's authors caution might be too young. The Steens, Imnaha, Grande Ronde, Picture Gorge and Prineville Basalts all erupted within the main eruptive phase. The Wanapum and Saddle Mountains Basalts, about 7 percent of the CRBG volume, were generated during the waning stage of the eruptions, with significant time gaps between members and flows. Single Wanapum flows are similar in volume to the large Grande Ronde flows, which commonly exceed 1,000 cubic kilometres; Wanapum lavas typically travelled many hundreds of kilometres from their vents as large pāhoehoe sheet flows, and most covered 50 percent or more of the Columbia Basin. Saddle Mountains flows are smaller (under 600 cubic kilometres), with time gaps between eruptions often exceeding 1 to 2 million years.

• Steens Basalt: the oldest formation, restricted to southeastern Oregon, formally recognized as the earliest CRBG formation in 2013; nearly 1 km thick at Steens Mountain
• Imnaha Basalt: Rock Creek type present in northeastern Oregon and southeastern Washington; erupted in the main eruptive phase
• Grande Ronde Basalt: 71 percent of total CRBG volume; eruptions estimated at about 16 to 15.6 million years ago, an interval that might be too young
• Wanapum and Saddle Mountains Basalts: about 7 percent of the volume, erupted in the waning stage; Saddle Mountains flows under 600 cubic kilometres, with gaps often exceeding 1 to 2 million years

Some CRBG flows advanced westward through a lowland gap in the Cascade arc, spreading into the Willamette Valley and Coast Ranges, and farther west into offshore forearc basins beyond the coastline of northwestern Oregon. In the Dundee Hills of Yamhill County, Oregon, lava flows dating back 15 million years pushed into the area from northeast Oregon, depositing Columbia River basalts and restructuring the landscape with hills and broken ridges. The reddish color in the Dundee Hills soil is derived from the Columbia River basalt lavas, including the Jory soil series, which cover approximately 80 percent of the area. These lava-based soils decompose quickly with the high rainfall of northwestern Oregon, which helps produce the Jory series of reddish silt, clay and loam soils, found predominantly on the eastern side of the Dundee Hills. The sedimentary Willakenzie soil series covers the steeper slopes of the western side, and a smaller amount of Jory soil exists on that side where the Columbia River lava flows cover the sedimentary formations. In the Tualatin Hills, the Laurelwood soils are derived from weathered basalt and loess and are fine, silty soils with no rocks. The soils reach depths of up to 100 feet. In the Laurelwood District, the Laurelwood soil consists of loess combined with basalt that is older than the basalt found in the Laurelwood soil of the Tualatin Hills.

• Some CRBG flows passed through a lowland gap in the Cascade arc into the Willamette Valley, the Coast Ranges and offshore forearc basins beyond the coastline of northwestern Oregon
• Dundee Hills: the reddish soil color is derived from Columbia River basalt lavas, including the Jory soil series, which cover approximately 80 percent of the area
• Jory: reddish silt, clay and loam soils, found predominantly on the eastern side of the Dundee Hills; the sedimentary Willakenzie series covers the steeper western slopes
• Laurelwood: derived from weathered basalt and loess; fine, silty soils with no rocks, up to 100 feet deep in the Tualatin Hills

The major physiographic feature of the northern part of the province is the Columbia Basin, a broad structural basin lying between the Cascades arc and the Idaho batholith and covering more than 150,000 square kilometres. Washington's Columbia Valley AVA has soils defined by the Missoula Floods; most vineyards lie below the floodwaters, with soils of loess, windblown deposits of sand and silt, overlying gravel and slackwater sediment, with basalt forming the bedrock. This basalt can be thousands of feet thick, with a weight so heavy that some areas of the Columbia Basin are below sea level. The Missoula floods of the Pleistocene, released from Glacial Lake Missoula, created the Channeled Scablands, and at Palouse Falls the Palouse River has eroded through the Wanapum Basalt and the upper portion of the Grande Ronde Basalt. The northern part of the province is also folded: its large folds are best developed in the Yakima Fold Belt of central Washington and in the Blue Mountains anticlinorium of northeastern Oregon. Red Mountain is an anticline of the Yakima Fold Belt, with elevations from 500 to 1,500 feet, and its soil is sandy loam and gravel with a high alkalinity (high pH) and a rich calcium carbonate content. In the Walla Walla Valley, most soils are well-drained, sandy loess over Missoula Flood slackwater deposits and fractured basalt; above 1,200 feet, the maximum height of the Missoula Floods, soils are simply loess over fractured basalt. An ancient cobblestone riverbed defines the area to the south, The Rocks District of Milton-Freewater AVA in Umatilla County, Oregon, which lies entirely within the Walla Walla Valley AVA. Approximately 96 percent of The Rocks District is covered with soil from the Freewater series, which contains large amounts of loose, uncemented gravel, cobbles and boulders in very deep layers; roots can penetrate 30 feet or more before hitting bedrock or cemented soil. The Wahluke Slope, bordered by the Columbia River, the Saddle Mountains and the Hanford Reach National Monument, sits on a large, ancestral alluvial fan, with deep, wind-blown sand topsoil more than 5 feet deep on average.

• Columbia Valley AVA: loess overlying gravel and slackwater sediment, with basalt forming the bedrock; most vineyards lie below the Missoula floodwaters
• Red Mountain: an anticline of the Yakima Fold Belt; sandy loam and gravel soil with high pH and a rich calcium carbonate content
• Walla Walla Valley: sandy loess over Missoula Flood slackwater deposits and fractured basalt; above 1,200 feet, loess over fractured basalt
• The Rocks District of Milton-Freewater: about 96 percent Freewater series soil, with loose, uncemented gravel, cobbles and boulders; roots can reach 30 feet or more

Primary sources: U.S. Geological Survey, Scientific Investigations Report 2017-5022-N, Field-Trip Guide to the Vents, Dikes, Stratigraphy, and Structure of the Columbia River Basalt Group (Camp, Reidel, Ross, Brown and Self, 2017): https://pubs.usgs.gov/sir/2017/5022/n/sir20175022n.pdf; TTB final rules (Federal Register via govinfo.gov) for the Dundee Hills (69 FR, November 30, 2004), Tualatin Hills and Laurelwood District (85 FR 34095, June 3, 2020) and The Rocks District of Milton-Freewater (80 FR, February 9, 2015) viticultural areas, whose soil and size figures are the petitions' figures as the rules summarize them: https://www.govinfo.gov/content/pkg/FR-2004-11-30/pdf/04-26330.pdf, https://www.govinfo.gov/content/pkg/FR-2020-06-03/pdf/2020-10919.pdf, https://www.govinfo.gov/content/pkg/FR-2015-02-09/pdf/2015-02553.pdf. Washington State Wine Commission: https://www.washingtonwine.org/grapes-soil-sun/, https://www.washingtonwine.org/resource/columbia-valley-ava/, https://www.washingtonwine.org/resource/walla-walla-valley-ava/, https://www.washingtonwine.org/resource/wahluke-slope-ava/, https://www.washingtonwine.org/resource/red-mountain/. Last verified 2026-11-09