Tuesday, June 21, 2016

City of Rocks National Preserve in Idaho has the Window Arch, a rare granite arch



The City of Rocks is an out-of-the-way National Preserve in south-eastern Idaho where granite spires, domes, and loaves seem to pop out of the rolling plains. Historically, this area is famous for the pioneers on the California Trail heading west and having this landmark serve as a special stop along the way. Many of the pioneers signed their names on the granite rock using axle grease. This place is also famous with climbers for some of the clean granite rock that makes for excellent climbs. We climbed one of the easier climbs in the area before taking lots of pictures. Since granite rarely forms arches, we made a point of looking for this feature, Window Arch. It's right next to a parking area for camping off of the main road through the area. Window Arch appears to be on the verge of falling down. The horizontal pieces of the arch have split and are offset from each other. It looks like either or both sides could some day soon slide past the other and collapse. Granite might form arches when sheets of granite flake off in a process called exfoliation. If both sides of a dome-shaped granite rock flake off, there may be left behind the highest part of the dome or loaf left behind, thus making an arch.

This image was made by merging two images together to increase the amount of detail in the final image. Both images taken at ISO 100, f8.0, 1/180 sec. with a Canon Rebel xSi, with a focal length of 18 mm. Rick made a point of composing this image so that the sky and top of the tree would be clear of the underside of the arch.

Remember, it's not just a picture, it's a story!

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