The Caves:
The Sand Caves outside of Kanab were not formed naturally. They are the remnants of a short-lived mine that existed in the 1970s to extract sand from the soft sandstone for use in glassmaking. That soft sandstone is a variety called Navajo Sandstone, and is the famous Red Rock that Southern Utah is known for.
The Lesson:
Around 190 million years ago, during the Early Jurassic period, the area that is now the Colorado Plateau was covered in the largest known sand desert in Earth's history. While most of the sand from the dunes of that early desert would not turn into sandstone, the bottom layers would. Those layers would come to form what is now the sandstone. They sand was compressed into stone by the pressure from the sand above and mineral-rich groundwater. As the water percolated through to the water table, the minerals, primarily clacium carbonate, were left behind, gluing the sand together into sandstone.
Navajo Sandstone showcases something called "Cross-bedding". It means that the pattern in the stone's band slopes downward in the same direction that the wind was blowing. Cross-bedding can be seen in sand dunes today, as well as in this sandstone.
Sandstone gets its color from the minerals around it during its formation. There are several colors that sandstone can be: Tan, brown, yellow, white, red, gray, and far more rarely, blue, green, and purple.
So what causes the colors?
Quartz: White or tan sandstones
Iron/Rust: The iconic Red Rocks, though it can also lead to brown.
Limonite: Yellow
Manganese: Purple
Clay: Gray or blue
Nothing: A lack of minerals would lead to white or sandy coloration.
The Questions:
1. Notice the color of the sandstone here. Which mineral do you think was the most prominent in the formation of this sandstone?
2. You might have to do this one from outside the caves, near the trail. Take a look at the rock layers. What direction are they tilting? What can you infer from this about the winds in the Jurassic desert?
3. To deter armchair cachers, please include a picture in your log of the caves.