WARNING!!!
Before attempting this EarthCache please check the weather. This EarthCache will take you into the normally dry creekbed of Cibilo Creek. It does not have to rain here for this area to flash flood.
To get to the Earthcache
The easiest and shortest way to get to this Earthcache is to use the parking coordinates in the waypoints below. There are stairs going down from the park into the creek. If you’re more adventurous you walk from my other Earthcache, GC933NP Selma Stage Stop Park Erosion.
Before you go…
It would be easier to study this picture on a computer. It can be done on a cell phone. But bigger screens make this easier. Consider taking a ruler with you to the Earthcache.
This picture was taken by NASA’s Mars rover Curiosity. Examine the picture closely. Pay attention to the scale. You’re not looking at big stuff!
As you go…
When you’re in the bed of the creek, pay attention to the rocks. Note their sizes and shapes. As you near ground zero you should notice the layers of sediment in the bank. Pay attention to what you see there.
How are pebbles formed?
Pebbles range in size from 4 to 64 mm or 0.16 to 2.52 inches in size. They are rocks that have been rounded from being transported downstream by water. You will see them congregated in areas where the water moves too fast for smaller particles such as sand to stay. They are usually seen where the currents are the fastest.2
This area of the creek is normally dry, with a few pools or ponds scattered about. When it does rain, water rushes through here at a pretty quick pace. It would not be a good place to be standing after it rains upstream!
How to log this EarthCache
Please send me a message (my preference) or email me with the GC code and name of this EarthCache. Answer all of the following questions. No Armchair caching, you must visit the site. Include a picture of you (or part of you) taken some time while making observations for this EarthCache. You may go ahead and log after messaging/emailing me. Please DO NOT post the answers in your log. Thank you for visiting!
From the observations you made at the EarthCache location, answer the following questions.
1. What shape are the majority of the rocks you see?
2. What is the approximate size of the rocks you see in the creek bed?
3. Are these rocks pebbles?
4. What is the approximate size of the rocks you see in the creek bank?
5. Are these rocks pebbles?
But wait, there’s more! Planetary geologist use what they learn on Earth to study what is seen on planets. They make an analogy. So, compare what you saw at the EarthCache and to the picture above from Mars and answer the following questions.
6. Do the rocks in the picture look similar to what you saw at the EarthCache?
7. Are these rocks pebbles?
8. Do your answer for questions 6 and 7 indicate there may have been water on Mars?
9. If you think there was water at the location in picture of Mars, do you thik the water velocity was zero, low, or high? Why?
10. Could something else have created the shapes?
Sources
1 - NASA online, https://mars.nasa.gov/news/1477/pebbly-rocks-testify-to-old-streambed-on-mars/
2 - Encyclopedia Britannica online, https://www.britannica.com/science/gravel#ref65729