page_title: Columbia River Basalt Group
section_title: Steens Basalt
hierarchical_section_title: Columbia River Basalt Group / The major Columbia River Basalt Group flows / Steens Basalt
caption_attribution_description: English: Steens Mtn, view from the top towards the Alvord Desert
context_page_description: 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 mainly eastern Oregon and Washington, western Idaho, and part of northern Nevada. The basalt group includes the Steen and Picture Gorge basalt formations.
context_section_description: The Steens Basalt flows covered about 50,000 km² (19,000 sq mi) of the Oregon Plateau in sections up to 1 km (3,300 ft) thick. It contains the earliest identified eruption of the CRBG large igneous province. The type locality for the Steens basalt, which covers a large portion of the Oregon Plateau, is an approximately 1,000 m (3,300 ft) face of Steens Mountain showing multiple layers of basalt. The oldest of the flows considered part of the Columbia River Basalt Group, the Steens basalt, includes flows geographically separated but roughly concurrent with the Imnaha flows. Older Imnaha basalt north of Steens Mountain overlies the chemically distinct lowermost flows of Steens basalt; hence some flows of the Imnaha are stratigraphically younger than the lowermost Steens basalt.
  One geomagnetic field reversal occurred during the Steens Basalt eruptions at approximately 16.7 Ma, as dated using  ⁴⁰Ar/³⁹Ar ages and the geomagnetic polarity timescale. Steens Mountain and related sections of Oregon Plateau flood basalts at Catlow Peak and Poker Jim Ridge 70 to 90 km (43 to 56 mi) to the southeast and west of Steens Mountain, provide the most detailed magnetic field reversal data (reversed-to-normal polarity transition) yet reported in volcanic rocks.
caption: View from the top of Steens Mountain, looking out to Alvord Desert with basalt layers visible on the eroded face.
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