12/28/2023 0 Comments Sea stack picturesUnlike most of the CRBG, the Picture Gorge Basalt originated in central Oregon, not too far from here–there’s a whole swarm of dikes near the town of Monument, Oregon. And the next youngest unit of the CRBG was the Picture Gorge Basalt, shown capping the ridge in the background. Picture Gorge Basalt at the Painted Hills. Steens Mountain is one of our state treasures –it’s a fault-block mountain, uplifted by Basin-Range extension along a normal fault along its eastern side. The CRBG started with eruption of the Steens Basalt about 16.7 million years ago, which makes up the upper 3000′ or so of Steens Mountain, shown here. –and at the bottom, I’m adding a short glossary to explain some of the terms. We learn all these things and we put them in some part of our consciousness that doesn’t really let them soak in –but once in awhile they do.įinally, the CRBG is beautiful and forms beautiful landscapes! Below are some photos to illustrate it, from feeder dikes in eastern Oregon to sea stacks eroded from a giant sill on the coast.Īnd I’ll save my snarky comments about young earth creationism for another post. That’s what I find so wonderful and amazing about geology. And… (here’s the outrageous part), on reaching the Pacific, many of the flows re-intruded into the existing sediments and sedimentary rocks along the coastline to form their own magma chambers, some of which were thousands of feet thick! AND… some basaltic magma from those chambers then re-intruded the country rock to form dikes –and some even re-erupted on the seafloor!Īll these outrageous details. And… many of the lavas made it all the way to the Pacific Ocean. It also erupted over a fairly short period of time: from about 17 million years ago to 6 million –but 96% of it erupted between 17 and 14.5 million years ago.Īnd… most of it erupted from fissures in eastern Oregon and Washington –the roots of which are now preserved as dikes. For one thing, it really is huge: it covers an area of more than 77,000 square miles with a volume of more than 52,000 cubic miles –that’s more than 50x the volume of air between the north and south rims of the Grand Canyon! Really-the National Park Service estimated the volume of “Grand Canyon Air” to be about 1,000 cubic miles. With views like this, how can you say the CRBG is boring? (Photo “F” on map below.)īut of course, the CRBG is outrageous for a whole host of other reasons. Lava flows of the CRBG in northern Oregon and Mt.
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