Smith Rock Earth Cache EarthCache
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All earth caches require answering questions to claim them. You will find the questions for this cache at the end of the listing. (To claim this cache:) You can park less than 500 feet from the coordinates and access them by paved path. There is only an elevation change of a few feet. It is wheelchair accessible. There is a day use fee of $5. per vehicle.
The coordinates for this cache take you to a location inside of Smith Rock State Park. It is one of the most spectacular and accessible rock formations in Oregon. It can be visited any season and you can drive to within a short distance of the cache in any car. There is a day use fee, at this time $5, but the view alone is worth it, and there are several beautiful walks or hikes to be taken. There are also, at this writing, fifteen traditional geocaches within the park. The coordinates can be accessed entirely by official paths, so please do not cut across natural areas.
If you had been watching this location 29 million years ago you would have witnessed explosive volcanic eruptions. The area of what is now Smith Rock State Park was inside a great volcano. Those violent eruptions eventually emptied out the interior of the volcano and it collapsed in on itself. A giant caldera was formed. Some other calderas in Oregon are Crater Lake and Mount Newberry. This caldera is a different kind than those, called a resurgent caldera. The caldera, named the Crooked River Caldera, was about 22 miles by 15 miles and stretched from here to beyond Prineville. More information about the Crooked River Caldera is available by doing an online search.
Later eruptions inside of the caldera started the formations that you see at Smith Rock State Park, and many others around the area. These formations are made from two different kinds of rock. The main one is called welded tuff. Welded tuff is created when an eruption of volcanic ash and pieces of volcanic rock is so hot that they weld together as solid rock when they settle and cool. Most of the rock across the river from you is welded tuff. If you get close to it you can see that it is a mixture of fine material and chunks of rock. The other rock type is called rhyolite. The dark colored rock across the river from you is rhyolite. It was formed when silica rich lava was forced up, like toothpaste from a squeezed tube, and cooled. Rhyolite is not always that dark and can be a variety of colors. In fact, the light colored rock sticking out of the trail as it starts down into the canyon is also rhyolite, as is the rock directly below the overlook.
The forces of weathering and erosion have reshaped the original rock to the form you see now. Weathering is a term for the action of breaking rocks apart. Erosion is when the pieces are carried away.
There are several forces that are weathering the rocks here. One important force is ice. Water seeps into the cracks and spaces in the rocks. When it freezes it expands and wedges apart the rock. This can happen on a large scale, breaking away big chunks if rock, or on a small scale, crumbling the rock into sand and dust. Another important force is plants. Have you ever seen cracks in a sidewalk caused by growing tree roots? Plant roots do the same thing here. Seeds fall into cracks. As they sprout and grow, the roots wedge the cracks wider. The rock eventually breaks apart. On the surface of nearby rocks you can see colored crusty growths. These are called lichen, pronounced liken. As the lichens grow they use acids to dissolve the rock surface for nutrients. These forces and others have been crumbling the rocks. Across the river you can see the crumbled and broken rock at the base of the cliffs.
The Smith Rock tuff and rhyolite formations were once much larger. As they have been weathered, the pieces have been eroded away. The most important forces of erosion here are gravity and water. Gravity pulls the broken pieces downhill. Water from rain and snowmelt washes the pieces downhill. The Crooked River has been carrying the dust, sand, and rock pieces away, down river.
All of this had been going on for millions of years when another volcano added new rock. About half a million years ago a different kind of lava flowed from Newberry Volcano, south of where Bend is today. This lava was low in silica and therefore more fluid. Instead of erupting explosively, it flowed for great distances across the plateau and along river canyons. When it got to these welded tuff and rhyolite formations, the lava flowed over the low ones and up to the taller ones. When the lava cooled it formed a gray rock called basalt. Where you park your car is on top of the layer of basalt. When you walk to these coordinates you drop below it. Look behind you and to your right and left to see the basalt rim.
To claim this cache:
1. Post a photo of yourself or your group holding your GPS unit or units. Include enough of the Smith Rock formations in the background to be recognizable. (Posting a photo is now optional.)
2. Email us the answers to the following questions. Do not post the answers in your online log.
According to the sign, how thick was the volcanic material deposited here by eruptions?
What are two of the colors you can see in the rock formations across the river?
According to the sign, how did the more recent basalt flows effect the Crooked River?
Additional Hints
(No hints available.)