Balanced Rock EarthCache

Hoodoos are formed by two weathering processes that continuously work together in eroding the edges . The primary weathering force at is frost wedging. Here we experience over 200 freeze/thaw cycles each year. In the winter, melting snow, in the form of water, seeps into the cracks and freezes at night. When water freezes it expands by almost 10%, bit by bit prying open cracks, making them ever wider .
In addition to frost wedging, what little rain we get here also sculpts the hoodoos. This weak carbonic acid can slowly dissolve sandstone grain by grain. It is this process that rounds the edges of hoodoos and gives them their lumpy and bulging profiles. Where internal mudstone and siltstone layers interrupt the sandstone, you can expect the rock to be more resistant to the chemical weathering because of the comparative lack of sandstone.
Many of the more durable hoodoos are capped with a special kind of magnesium-rich sandstone called dolomite. This sandstone has a different color and texture than the soil. Dolomite, being fortified by the mineral magnesium, dissolves at a much slower rate, and consequently protects the weaker sandstone underneath it in the same way a construction worker is protected by his/her hardhat. Rain is also the chief source of erosion (the actual removal of the debris). In the summer, monsoon type rainstorms travel down the mesa tops and erode the soil around the rock. Preservation Message: Unfortunately hoodoos don't last very long. The same processes that create hoodoos are equally aggressive and intent on their destruction. The average rate of erosion is calculated at 2-4 feet (.6-1.3 m) every 100 years
Send me the answers to these questions.
1. What kind of material is the top?
2. What kind of material is the bottom?
3. looking around What is the greatest source of erosion?

Contacted BLM Farmington office and they said as long as it is not near private land it was ok.