Picture by
David A
G Wilson. Re-used under the terms of the
Creative
Common license
The cache is located in a Travis County preserve. It has been
approved by Travis County Park Rangers. At all time, please respect
the preserve rules. In particular, please always stay on the
trails, obey the signs and do not leave anything behind. Pets are
not allowed.
At time of approval, there is $8 entrance fee per vehicule. You
will need to pay the entrance fee to proceed to the cache. A 1/2
mile round trip hike will be required to claim the cache. For more
information on the park, check the
Travis
County website.
Definition
A plunge waterfall is a waterfall where the water descends
vertically, losing contact with the bedrock
surface. |
Geological context
Hamilton Pool is part of the area of Central Texas known as the
Edwards Plateau. Rocks in the region are various types of
sandstone, limestone, dolomite, and shale, all of which were
deposited in an ancient ocean below sea level about 100 million
years ago (Cretaceous Period). At the edge of the plateau is the
Balcones fault line through which softer rock (to the southeast)
eroded at a faster rate than rock above the fault line.
Hamilton Pool's formation
When a river flows over a step in the rocks created by a fault line
it creates a waterfall. Over time, the edges of the hard rock layer
on top (cap rock) will gradually break away and the waterfall will
steadily retreat upstream, creating a gorge or canyon.
When the rock layer below the cap rock of a waterfall is of a
softer type, it erodes much faster due to the splash back. This is
called “Undercutting”. The Undercutting will form a cave-like
formation known as a rock shelter behind the waterfall. Under the
waterfall, a plunge pool will also form. In some instances, the
depth of a plunge pool may nearly equal the height of the cliff
causing the falls. As the undercutting continues, blocks of rock
overhanging under the resistant cap rock layer collapses to the
base of the waterfall. Over time, by action of attrition and
abrasion, these rocks are brocken into smaller rocks that make
their way to the bottom of the pool. As they swirl at the bottom of
the pool, they make it wider and deeper.
Hamilton Pool is the archetype of a plunge pool.
Hamilton Pool today
Because the water level stays relatively constant in the pool even
in drought conditions, the canyon is a very unique ecological
environment. Several rare plant species including canyon
mock-orange, red bay (western-most colony of this eastern species),
and chatter box orchid are known to occur in the canyon areas along
Hamilton Creek.
Logging Requirements
In order to claim this earthcache, you will have to complete the
following 4 tasks:
- Task #1: Go to N 30° 20.508 W 098° 07.799. This is the trail
head going to the pool. Using your GPSr, determine the altitude in
feet at this location. Please email the answer.
- Task #2: Follow the trail to the falls. Go to the little sandy
beach on the north side of the pool. Take a picture of yourself
with the waterfalls in the background. Please attach the picture to
the log.
- Task #3 From the beach, use your GPSr to determine the altitude
in feet at this location. Please email the answer.
- Task #4 What type of trees do you find the most in the canyon
by Hamilton creek and why? Please email the answer.
As earthcache guidelines require, please complete all of the
mandated tasks, post your picture and send me the email in a
reasonable amount of time or your log will deleted per rules (I
really do not want to have to do that).
Remember 4 tasks:
- Email the altitude at the trail head.
- Log your picture from the beach.
- Email the altitude at the beach.
- Email the name of the type of tree at the bottom of the canyon
and the reason they are there.
Enjoy the hike!
3/22/09 Update:Please note that the park can close after
heavy rain. Please always call ahead to ensure the park is open.
Swimming can also be restricted based on bacteria level. Another
good reason to call ahead.
Reference: