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Rockhounding on the Stillwell Ranch, Southwest Texas
By Jim Miller

February 2012

In late February I spent a week in southwest Texas to explore a part of the USA
that I had never visited before. A friend of mine from Oklahoma, Neil Garrison,
met me at the Midland airport and we drove about 4.5 hours to our lodging
destination at the Stillwell Ranch. The ranch is located just outside the northeast
border of Big Bend National Park and includes thousands of acres of “old west”
ranchland. This very remote and picturesque part of Texas has a fascinating and
colorful history, much of which is explained in the small museum located at the
ranch. The ranch also has a small general store and camping spaces for RVs
and tents. An Internet search will provide you with more information about the
ranch and its history.
Neil and I don’t have a RV, but we had arranged to stay in the “bunkhouse” on
the ranch. It wasn’t luxurious, but this old trailer served our needs and was our
home for the week.


Our primary goals in visiting this interesting part of Texas were to hike and
explore the wonders of Big Bend National Park. We made numerous excursions
to see the highly variable geology, terrain, archeology and ecology within the
park boundaries. Back at the bunkhouse in the evening, we met several of the
other visitors who had traveled to the Stillwell Ranch in their RVs. We learned
that a couple of these folks were repeat visitors, and that their primary purpose in
traveling to the ranch was to go rockhounding! Although I was aware that the
geology of the area was quite interesting, I had no idea that the Stillwell Ranch
catered to rockhounds. Now, this visit to Texas was getting even more

Upon inquiry, I learned that the most productive rock collecting location was on
the gentle hillsides near the “black water tank” about 5 miles east of the Stillwell
Store. One of the rockhounds visiting the ranch offered to take Neil and me on a
collecting trip the following morning. We happily accepted the offer. There’s no
better way to learn about an area than to have a knowledgeable guide show you
the way!
During our adventure to the water tank area, we learned that the primary
objective of the rockhounds was to find high quality plume agate, moss agate
and colorful jasper. These desirable lapidary rocks are found within ancient
gravel terrace deposits that cap some of the ridges and hills in the area. The hills
in the middle distance in the photo below show the terrain on the Stillwell Ranch
where the gravel terrace deposits occur.


Once we arrived at our destination near the black water tank, we found that the
terrace gravel consisted of an enormous variety of rocks. The terrace deposit
represents the remnants of ancient erosion of several thousand feet of
sedimentary and volcanic rocks located to the north. The gravel and cobbles
exposed on the ground, between the thorny brush and cactus, included finegrained
basalt, rhyolite, tuff (heat-welded volcanic ash), limestone, chert, petrified
wood, chalcedony, agate and jasper.
The agate and jasper represented only a tiny fraction of the terrace gravel, the
proverbial “needle in the haystack.” But there was a secret to spotting the good
stuff. The chalcedony, agate and agate-rich zones of jasper typically had a thin,
white oxidation/hydration layer, or patina, on the outer surface of the agate. The
piece of translucent agate below shows how this opaque patina forms a white
skin on the rock. The secret to success was spying rocks that had white patina,
or patterns of white, on a rock that was otherwise gray, red or brown.

The photos below show two different sides of the same piece of banded jasper.
The top photo shows the side of the rock that was exposed at the surface. Note
the white patina following the more agate-rich seams in the stone. The second
photo shows the interior of the rock and the typical thickness of the patina skin.


In two separate visits to the collecting area and a total of about 6 hours of hillside
wandering, I picked up about 40 pounds of beautiful rock from Stillwell Ranch
property. The ranch charges a mere 50 cents per pound for raw rock that you
find and remove from the property. Neil was kind enough to mail my treasures
home by USPS Priority Mail.
The variety and quality of jasper and agate that I found was amazing. The jasper
typically is mixed with at least 10 percent agate in exquisite swirls and plumes.
Three of the whole rock pieces that I found are show below.



Of course, I couldn’t wait to slice up some of this beautiful rock at home. The
photos below show slices of some of the varieties of jasp-agate and moss agate
that I found in the terrace gravel. WOW! You can get lost in the color and
complexities of the moss agate.




People have searched for useful stone in the hills of the Big Bend area for
thousands of years. Native Americans traversed the area for millennia seeking
stone that could be used to make sharp-edged tools like knives and arrowheads.
While searching the slopes, I often found discarded stone flakes that had been
removed from rocks in the past to test their color and workability. Many of these
flakes were made by recent visitors, but some of the flakes had significant patina
on them, indicating that they were quite old and made by Native Americans. The
photo below shows a jasper biface (or preform) that I spotted peeking out of the
ground in a small erosion channel on one of the hillsides. This piece of flaked
jasper is likely several centuries old.


I understand why the Native Americans were interested in some of the stone
varieties in the gravel terrace deposit. Much of the agate, jasper and petrified
wood flakes very well. The photo below shows a colorful collection of
arrowheads that I made out of rock that I found at the Stillwell Ranch.

Most of you readers are lapidary enthusiasts, not flintknappers. The photo below
shows a sphere that Dennis Borden made for me out of the center of the largest
piece of moss agate that I found on the Stillwell Ranch. Nice!

The Big Bend area of Texas is a long way from most places, but it is well worth
the visit. The remoteness of the area means that the Stillwell Ranch property
doesn’t get excessive pressure from rockhounds. Erosion from occasional flash
floods in the area assures that new rocks are gradually exposed on the terrace
slopes. So, if you ever visit the Big Bend area, don’t forget to go rock collecting
at the Stillwell Ranch. Now that you know what to look for, you won’t be

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