What Is The Cove Made Of?

David Pearson VEA 2015

Notice the straight line of rimrock behind David’s head.

David Pearson, Visitor Experience Assistant, has a passion for geology and has been sharing The Cove’s volcanic past with campers this summer.  For those of you who can’t come to David’s evening campfire programs, here is just a glimpse of what The Cove is made of…

The Geology of where the Crooked, Deschutes and Metolius rivers meet is fascinating indeed. When in these canyons, one can’t help but notice the different layers in the walls and wonder how they formed. The geologic history of the area goes back 50 million years. However, most of what we are able to see within the cannon walls dates back about 10-12 million years ago. There are three prominent formations that stick out; the Deschutes Formation, the Rimrock Basalt and the Intracanyon Basalt. The oldest of the three is the Deschutes Formation. This is the softer lighter layers in most cases, but it can also be dark grey. In it we see layers of ash, pumice, sandstone and river stone conglomerates. The Rimrock Basalt covers most of the very top of all the layers except “The Island” and the bench that the Crooked River Campground is on. Round Butte to the north of the park contributed greatly to the Rimrock Basalt. The average distance between the Rimrock and the water is between 600 – 800 feet.  Notice that the height of the Island is about 200ft lower in elevation than the rest of the canyon walls. That is because these were formed by the Intracanyon Basalt flows that happened after the Rimrock flows in areas of the canyon that had already eroded. As many as 15 different Intracanyon flows happened in rapid succession. These traveled all the way from the Newberry Crater area and started to cool by the time they came in the vicinity of the modern Round Butte Dam. As the lava cooled it created a natural dam and back flowed several miles up the Crooked and Deschutes rivers. The Island is composed entirely from Intracanyon basalt. It is the columnar jointing (or palisades) on the Island that inspired the name for the park. The basin that The Cove Palisades lies in has throughout its geologic history been covered by lava, water and ash. The relentless force of these rivers has repeatedly eroded all this ash and lava and carved out the beautiful canyons we see today. If you take a moment you can read the walls and take a trip back in time.

DSC_0074On the left notice the softer lighter layers of the Deschutes Formation. This had already begun to erode significantly by the time of the Intracanyon Basalt follows that we see on the right.

About coveranger

"One's happiness depends less on what he knows than on what he feels." - Liberty Hyde Bailey

Posted on August 22, 2015, in Geology, The Park and tagged , , . Bookmark the permalink. Leave a comment.

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