Benbrook Lake Fossil Hunt EarthCache
Hidden : 1/12/2010
Difficulty:
3 out of 5
Terrain:
2 out of 5

Size: Size: not chosen (not chosen)

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Geocache Description:

Requirements for claiming a find.

1. Take a picture of yourself in the spillway area and post the image.
2. Find and take a picture of a fossil and post the image. This fossil does not have to be a ammonite.
3. Estimate how far below the general area the spillway bottom is and email it to me. Please do not post this answer in your log. This will show how far below the general surface these rocks are that contain the fossils.

If these requirements are not met your log may be deleted.



Benbrook Lake History

Construction on the lake began in May 1947, and was practically completed when floodgates were closed and deliberate collection was begun in September 1952. The rolled-earth embankment is 9,130 feet in length, including the concrete spillway, and rises 130 feet above the streambed to an elevation of 747 feet above sea level. A pair of 6.5 by 13-foot sliding gates operated by electric cable hoists controls the floodwater releases through the 13-foot diameter conduit. Two 30-inch diameter pipes are provided for low-flow releases to maintain downstream river flows. The concrete spillway for uncontrolled releases is 500 feet long, with a 100-foot notch in its center.

At the normal, or conservation pool, level of 694 feet above sea level, the lake covers 3,770 surface acres. This would increase to 7,630 acres if the lake ever reaches the nominal maximum flood pool elevation of 724 feet, which is also the overall spillway elevation at the top of the center notch.



Flooding History

Flooding at Benbrook Lake has flown over the spillway 5 times. During these floods the water has only ever flown over the 100 foot notch in the center of the spillway. Below the spillway the water from these floods has created an area that is a prime area for fossil hunting. Much of the rock that underlies Tarrant County consists primarily of seventy to eighty-five million year old sedimentary rock strata from the Late Cretaceous Period. These Goodland Formation limestones are roughly contemporary with the last dinosaurs on land, during the Mesozoic Era.

Accessible in the Benbrook Spillway cut these rocks are the remains of a shallow ocean that covered this part of the continent and receded over the last seventy million years to the present Gulf Coast shoreline in South Texas. It represents a shallow marine habitat, under about thirty feet of depth, which was populated by oyster reefs, corals, clams, sea urchins, and ammonites. It is very similar to what you might find off the Texas coast today at similar depth, except for the ammonites. Ammonites are an extinct group of shelled mollusks, related to the nautilus, squid and octopus. Most of the fossils you find have living descendants today, some in almost exactly the same form, like oyster shells.

Additional Hints (Decrypt)

N yvggyr jngre ba gur sbffvy zvtug znxr vg fubj hc orggre va lbhe vzntrel.

Decryption Key

A|B|C|D|E|F|G|H|I|J|K|L|M
-------------------------
N|O|P|Q|R|S|T|U|V|W|X|Y|Z

(letter above equals below, and vice versa)


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