Intracanyon flows of the Columbia River Basalt Group in the lower Columbia River Gorge and their relationship to the Troutdale Formation
Intracanyon flows of the Columbia River Basalt Group in the lower Columbia River Gorge and their relationship to the Troutdale Formation
Geological Society of America Bulletin (April 1984) 95 (4): 463-477
- alluvium
- Cenozoic
- clastic sediments
- Columbia Plateau
- Columbia River
- Columbia River Basalt Group
- distribution
- fluvial features
- geochemistry
- geomorphology
- gorges
- Hood River County Oregon
- igneous rocks
- Klickitat County Washington
- landform evolution
- lava
- lava flows
- Miocene
- Multnomah County Oregon
- Neogene
- neotectonics
- Oregon
- rivers
- sediments
- Skamania County Washington
- stratigraphy
- structural controls
- structural geology
- tectonics
- Tertiary
- United States
- uplifts
- valleys
- volcanic rocks
- Washington
- Troutdale Formation
- Columbia River Gorge
The Priest Rapids Member (Wanapum Basalt) and the Pomona Member (Saddle Mountains Basalt) of the Columbia River Basalt Group crossed the Miocene Cascade Range into western Oregon and Washington as intracanyon flows about 14 m.y. and 12 m.y. ago, respectively. A thick, allogenic, bedded palagonite complex underlying the Priest Rapids intracanyon flow originated when the first Priest Rapids flow interacted with a shallow lake on the Columbia Plateau, displacing water that flushed hyaloclastic debris into an incipient ancestral Columbia River channel. The Priest Rapids flow then overfilled the canyon, forcing the river northward, where it established the Bridal Veil channel. The Troutdale Formation is made up of (1) older alluvial gravels deposited below and above the Pomona intracanyon flow and (2) younger, more varied alluvial deposits characterized by clastic and hyaloclastic debris from Boring and High Cascade volcanism. The shift of the lower Columbia River to its present course took place during time of maximum alluviation. The present Columbia River Gorge was formed in post-Troutdale time by entrenchment of the Columbia River during rapid uplift of the Cascade Range of northern Oregon during the past 1 to 2 m.y.--Modified journal abstract.