This EarthCache will bring you high above the valley floor to a very popular place. It is a strenous hike to this point and you will need to be prepared. Make sure you have plenty of water and food for your hike and never hike alone. After you return to the safety, please send me the answers to the following questions:
1. In your own words, how did this fin form?
2. Describe what you see. Is it uniform? Texture? Do you see the fractures?
3. If it continues to erode, what will happen to this trail?
4. How does this fin compare to the other sandstone to your left and right (on next ridge)?
5. Post a picture of you (face not required) or a personal item at the fin.
What is a fin?
A fin is a formation that is a narrow piece of sedimentary rock, in this case sandstone, that remains after all the surrounding rock has been eroded way. This erosion occurs on the parallel joints or fractures of the rock. It will begin as a plateau that will have vertical cracks that are parallel to each other. Erosion will occur in two different manners. The first is when water will open the joints/fractures wider and wider. The second is when the surrounding rocks are harder and will cause the weaker rocks to fall away.
As the erosion continues, it will begin to form windows, arches, and eventually hoodoos. This can be simplified in a 4 part process. It will begin as a plateau when the uplift process creates deep, vertical fractures. As these fractures weather and erode, the fractures will enlarge and create fins. As erosion continues from the bottom, you will start to see arches and windows. And lastly, the windows and arches will weather further to cause collapsing, which will form spires or hoodoos.
So why does this fin form here?
Sedimentary rocks are bedded and provide zones where erosion and weathering can weaken the rock. Navajo Sandstone that occurs at this location is an iron oxide cement sandstone. This type of cement is fairly weak, but in arid regions it is more resistant. Since water is lacking in this type of region, the water will not weather the iron oxide cements.
Sandstone is a bedded rock and will have prominent joins and bedding planes that will channel the water. This will start to create angular patterns in the stone. And since there is not much soil here, the joints will control the water drainage and create steep slopes and drastic topography.
This EarthCache was approved by Zion National Park. Please do not deface or collect anything from this site.