Columbia River Basalt Group (Wikipedia)

This article incorporates some material from the USGS article Columbia River Basalt Group Stretches from Oregon to Idaho.

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The Columbia River Basalt Group is the youngest, smallest and one of the best-preserved continental flood basalt province on Earth, covering over 210,000 km2 (81,000 sq mi) mainly eastern Oregon and Washington, western Idaho, and part of northern Nevada. The basalt group includes the Steens and Picture Gorge basalt formations.

Paradise Valley Conservation Area (wta.org) This wild wood started out as a working farm and timber producing homestead over one hundred years ago. It became part of the Snohomish County Park system in 2000, and now is in the process of returning to the wild state it once was. We hikers can watch this dynamic landscape by following the many trails that run through it. The trails are all well signed and a map can be printed or downloaded to your smartphone from the Snohomish County Parks website. Hike the perimeter trails for a good sampling of the area and a nice hike of about 5 miles.

Columbia River Basalt Group Stretches from Oregon to Idaho (usgs.gov) The thick, layered lava flows of the CRBG erupted as flood basalts, which originate as some of the most highly effusive eruptions in the world. The CRBG sequence a classic example of flood basalt activity that erupted more than 350 lava flows from about 16.7 Ma to 5.5 Ma. The eruptions originated from a series of generally north-northwest-trending linear fissures, ranging from tens to hundreds of kilometers in length, located along the Washington/Oregon/Idaho border. The magma that fed these massive eruptions may have come from a plume-like upwelling from the mantle called a hot spot. Since the time of the CRBG eruptions, the North American plate has moved in a west-southwestwardly motion, and that hot spot is now believed to reside beneath Yellowstone volcano in northwest Wyoming.