Which Way is Up? EarthCache

Castle Rock is an example of Inverted Topography. The rock on top of this mountain was the bottom of a river millions of years ago. Surrounding areas have all been eroded by more than 300 feet while the erosion-resistant top layer of Castle Rock has remained largely unchanged. What used to be the lowest place around is now the highest!

At the listed coordinates, look toward the east. You can see several distinct layers of sedimentary rock with different characteristics. The topmost layer is relatively hard while the layer at trail level is very soft. The soft layer is eroding out from under the top layer, leaving an overhang.

The large chunks embedded in the sandstones are rhyolite. A volcano near Mt. Princeton erupted about 36.7 million years ago and spread very hot ash over a large area downwind. The ash was so hot that it melted together upon landing and formed a glassy rock called welded tuff. Castle Rock Rhyolite, also called Wall Mountain Tuff, has been found throughout Douglas County, up to 20 feet thick in places.

To log this earthcache, send email with answers to the following questions:

1. Estimate the size of the largest chunk of rhyolite you can see from the listed coordinates.
2. Was the sandstone on top of Castle Rock formed before or after the eruption near Mt. Princeton?
3. Based on the size of the grains in the visible layers, can you conclude anything about the size and speed of the river over the time period it took to lay down these layers?

In your log for this cache, include a photo of you and your GPS with the rock in the background. This serves as proof that you actually visited the earthcache location.

Logs without supporting documentation will be deleted!

References
Park Map
http://en.wikipedia.org/wiki/Inverted_topography