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Pedernales Falls EarthCache

Hidden : 03/20/2009
2 out of 5
2 out of 5

Size: Size:   not chosen (not chosen)

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Geocache Description:

Thank you CenTex geocachers for naming this earthcache as a finalist in the 2009 Austin Cache Awards!

It is truly an honor. Thank you.


Welcome to Perdenales Falls! This is a wonderful spot in the heart of Texas hill country, where you can see a whole bunch of rock in different and interesting configurations.

Once you have entered the State Park and made the drive down to parking, you will need to hike down the trail to get to the posted coordinates. About a quarter-mile down the trail, you will find an overlook. Here, you will enjoy a birds-eye panoramic view of the section of the river called the Perdenales Falls. Click here and here to see what's in store for you at the overlook.

The falls and pools that you see in front of you are formed on inclined beds of Paleozoic limestone of Pennsylvanian age (about 300 million years old). The limestone is very hard and nearly black, and has abundant white calcite veins and large fossil crinoid stems.

The bedding is inclined, as opposed to the flat-lying Cretaceous limestones that lie above the river. This inclination is significant, and should be very visible and obvious to you as you view the banks of the river. The rock has been heavily exposed here, and the different layers of rock show themselves distinctly. This spot is unique in that you can see such clearly defined layers of limestone at such stark inclination. These limestones are part of the southwestern flank of the Llano uplift. These layers were tilted by the uplift, and then eroded long before early Cretaceous seas of the 100 to 120 million years ago covered this area and deposited sands, gravels, younger limestones, and marine fossils.

The inclined limestone layers, in their function as the bed of the river, create a series of drops and pools, which you should be able to easily recognize as you stand above the river looking down. In fact, technically, this section of the river should not be classified as a "falls", but rather as a "rapids". It is a repeated series of inclined bedding planes with uptipped ends of the beds forming edges of the pools. Put it all together, it really is a rapids, just on a huge scale. During a period of large flash flooding, the appearance as rapids becomes much more obvious with the huge torrents of water causing severe currents and hydraulic forces. Basically, it becomes a rapids fitting for Paul Bunyan and his huge canoe.

Hopefully, when you visit, it will not be flash flooding, because you need to go beyond the overlook, and descend down the steps to the bed of the river. When you get down there on the rock, you will see some geological features that are called rock tanks, also called potholes, also called tinajas. By the way, you can click here to see my earthcache about tinajas.

Here at Perdenales Falls, a pretty good tinaja is located at N 30° 20.267' W 098° 15.114'. Here is a photo I took. There are plenty of them around here.


Be aware and safe! This area experiences flash floods, which can easily kill you! Within just a few minutes, the water conditions can change from a placid flow to a deadly torrent of rushing currents.

The flash flood waters that reach this spot are usually from rains that occur hours earlier at locations that are miles upriver from this spot. The weather at this location can be very pleasant with no indication that deadly flood waters are coming. Therefore, be cognizant of the weather conditions in the regions upriver when you visit this location.

When you are at the river bottom, be alert. If you detect the presence of muddied water or rising water, leave the area immediately and head to higher ground. Don't hesitate. Seconds matter.

Now, on to the requirements for completing this earthcache...


In order to claim this earthcache as a find, you must complete the following tasks.

Requirement #1 - Photo Of You: With your find log, you must upload a photo of yourself at the river bottom. Go to the posted coordinates (N 30° 20.277' W 098° 15.108') and take the photo there. The photo should be taken with you standing in the river bed, and with the rising river bed behind you in the background. Click here to see an example of the photo you need to post. I don't care about your GPSr being in the picture. Find logs without a photo will be deleted.

Requirement #2 - Determine Total Drop: At the coordinates, where you are standing in the middle of the river, you have an interesting perspective from which you can appreciate the vertical component of the river here. As you look to the east, you see that you are located significantly higher in elevation over the surface of that bottom-most pool over there. As you turn and look west, you see the river bed rising above you. Task: Using whichever method you prefer, measure or estimate the total drop in elevation, in feet, that water travels as it flows through this entire network of drops and pools. From the top to the bottom pool. Email the answer to me.

Requirement #3 - Determine Angle Of Inclination: Now, look north, over to the opposite side of the river. On the bank over there is a pretty awesome view. There, you will see heavily exposed layers of limestone that rise at a very defined angle - the inclination I've been talking about. An exposure like this is certainly something you don't see every day, and the magnitude and consistency of the inclination will probably surprise you. Task: Using whichever method you prefer, measure or estimate the angle of inclination of these rocks layers from a horizontal reference. Hint - use the surface of the water as your horizontal reference. Email the answer to me.

Requirement #4 - Count The Steps: Yes, I have one more for you. As you should have learned here, the system of falls here (or rapids), is comprised of a series of "steps" (an inclination in the rock bed down to a pool, followed by another inclination in the rock down to another pool, and so on). You can think of it as steps from the porch of your house down to the front yard. You may have five steps at your house, or you may have ten. Task: Determine the number of "steps" that make up this falls system, from the top to the bottom-most pool. There are different ways you could determine this. You could walk the length of the area and observe it up close, or you could try to discern and count them from up above, at the overlook. Email the answer to me.

Remember Your Requirements:
Photo Of You,
Determine Total Drop,
Determine Angle Of Inclination, and
Determine The Number Of Steps.

A Few Words About Logging This Earthcache:

All actions here should be common sense. Do not post answers in your on-line log. Logs that expose answers will be deleted. Also, logs not accompanied by email within a reasonable amount of time will be deleted per earthcache rules.

Like every other earthcache out there, there are simple tasks that need to be fulfilled. You need to perform the tasks to log the earthcache. They are very simple and basic, and they are designed so that anyone can do them, as long as you can get your body down to the river bed. If you don't do the tasks, then you can't log the earthcache.

Occasionally, on one of my earthcaches, someone tries to enter a find log without even attempting the tasks. Among the excuses I have heard are "I didn't read the page, so I can't answer the questions." O_o Huh?! Pretty simple - if you don't even read the page and work the questions, since that is what defines the earthcache, then how can you say you did the earthcache?

Don't be shy about it. If you are unsure about an answer, that is okay. Give it your best shot. I promise I will give you an A for effort. It is the lack of effort that doesn't fly. And by all means, taking a photo is easy. Please get that done.

Now get out there and have fun. Enjoy the other fun geocaches in this park as well. I hope you enjoy this great location!

Spearing, Darwin 1991 Roadside Geology of Texas. Missoula, Montana: Mountain Press Publishing Company

Additional Hints (No hints available.)