Rio Grande Gravels

[Sabre52]

Howdy folks,

One of our members ( jamesp) requested that I post a little geological info on the Rio grande gravels that are such a treasure trove for us Texas collectors of agate, jasper and pet wood.

I first found out about this stuff shortly after I moved to Texas when I was reading an old geologic survey report which I've long since lost but I've studied the area a bit including several field trips so here goes.

First off, the so called Rio Grande Gravels are actually the Uvalde Gravels as the geologic survey guy first found the outcrops south of Uvalde, Texas. They are ancient river deposits from pluvial periods ( periods of huge rainfall) when much larger rivers transected much of the South Texas Plains. The Rio Grande was one of these rivers but the Nueces and the Frio were also much larger way back then , maybe 1-5 million years ago. These rivers drained much of south and west Texas and of course lots of quartz gems found their way into the sedimentary gravel deposits which are now on the tops of terraces and plateaus in in the streams beds which drain these areas.

From a collectors point of view the collecting in these gravels is truly terrific as they contain material from almost every deposit found in northern Mexico and West Texas which are both areas rich in the gem materials we all love. The petrified wood specimens common in these deposits are often tropical forms found now mainly in tropical Mexico or South America. Lots of kinds of monocots like palm and fern, but also lots of hardwoods too. In addition, one can find banded agate, moss agate, flower garden agate, dendritic agate, plume agate, orbicular rhyolite, many of the wonderstone type rhyolites, lacy agate, many types of orbicular jasper, Devil's Toenails and other fossil rocks, flint nodules of almost every color or pattern, and lots of jasper in almost every color you can imagine. Unless water worn to remove the caliche ( limestone crust), the specimens are often hard to spot but the variety is truly unbelievable.

Anyway, I'm not a geologist so here's a link that contains more info on these neat deposits. Enjoy.......Mel

www.texasbeyondhistory.net/st-plains/nature/images/uvalde-W.html

[jamesp]

To me Mel,this Rio Grande event created the ultimate agate hunt and also an amazing geology study.Thanks for sharing this info.It should be interesting to many people.

[The Dad_Ohs]

Excellent article, thanks for the info!!

Something new to add to the wish list of places to go rock hounding!!

[riverbendlapidary]

Thanks for the link.

Also found dino bone and mastodon teeth. I love hunting Rio Grande stuff, never know what you are going to find and you can find stuff that resembles almost any type of agate or jasper found elsewhere. Someday when I get the time I'm gonna cut cabs from different agates from around the world and put them right next to their twin found in Rio Grande agate.

Also, don't forget this extends into West Texas. You can find good Rio Grande along and near the River south of Marathon over to Del Rio as well.

[beefjello]

Thanks for the info Mel.. sure would like to get out there someday for some hounding.

[Sabre52]

JR: I thought I had found dino bone and we have tracks in the area so why not bone, but after talking with Matt Dillon, I found out what I had was "dino bone wood" or "pocket rot wood". Fooled me. It sure does look like bone though. I'd love to find a hunk of Texas dino bone. What region did your example come from?. Yeah, I heard the Stillwell Ranch material is ancient Rio grande gravel too.....Mel

[riverbendlapidary]

There is alot of dino bone near Study Butte. Used to go to a ranch there years ago and there where whole bone sections sticking out of the coal hills along with all sorts of fossils and wood. The guy let us collect wood but no bone.

I'll have to dig out some of the bone I have found out from Eagle Pass. It is not wood, looks just like the grey/blue bone from Utah. A friend and I were also given some bone specimens by a pit operator. They were like calcified and looked kind of like whale bone.

[jamesp]

Sounds like a lot of experienced folks have a lot of respect for the Rio Grande.I have made two trips in my life to the west for agate hunt.When i hit the Rio it was all over.And that river is a long one.But ya can't collect at Big Bend section(cause Texas owns our rocks).

[jamesp]

Rio variety

Attachments:

[gingerkid]

Thanks for the excellent info on the materials found at the Rio Grande gravels, Mel. What are "Devils Toenails?" A fossil?

Woah at the color in your crushed basal "vomit," James!

[Deleted]

Wow, I thought I was the only one that had that kind of variety. Big Horn Basin was filled in by river wash from two mountain ranges, glacial push from Montana, a wrinkle from when the Big Horn Mountains decided they were not going any further and ash from Yellowstone park blowing it's top. Makes for some awesome hounding but it is difficult to find two pieces of the same thing except for quartz.

I would love to hound that area and also show you around up here. Well, maybe some day. Thanks to both of you for taking the time to teach us something.
Jim

[Sabre52]

gingerkid: Yep, Devils Toenails are a type of small fossil primitive oyster like bivalve. The spire part of the shell is kind of curled or curved so when cut in cross section, they look like toenails. So much in the Rio grande gravel from Eagle Pass, Texas that I cut it to sharpen my saw blades. When I have time, I'm thinking of photographing my Eagle Pass rough for a thread to illustrate the variety of material from these gravel deposits. Started to sort stuff yesterday but I had a big four hour ridge ride with the gang and came home so tired I just wanted to take a nap *L*. Ahh the joys of growing old....Mel

[jamesp]

Some more sawn Rio G pebbles

www.flickr.com/photos/67205364@N06/sets/72157627611858808/

[gingerkid]

Thanks, Mel! Sure would like to see what Devils Toenails look like.

Those are beautiful, James! Really like the one with the black plumes!

[Sabre52]

Wow James, great slideshow! Really nice variety of specimens there. All my material is from Eagle Pass, Texas and I've only ever found one of those beautiful green examples and never a single black plume or sagenite, at least from what I've so far cut.

Hope to get busy and take some pics after tomorrow's horse clinic. The trainers taking me and Hopper and my wife and her favorite mount out to teach them how to cross this one creek crossing where those dang horses always try to kill us. I should say I'll take some pics if I'm still whole after the lesson *L*.....Mel

[jamesp]

Go Mel!If you can handle that bird of prey i have great faith that you can handle the horse.The lake Mel,Falcon Lake when it is low especially.About the middle section is fine.Don't know about the rest of the lake. Be careful,you and your wife.

[snuffy]

Mel,my rockpiles here with LaGrange gravels contain chert,chert and more chert!Some great stuff found in that Rio Grande!

snuffy

[coloradocliff]

Nov 7, 2012 21:51:05 GMT -5 jamesp said:

To me Mel,this Rio Grande event created the ultimate agate hunt and also an amazing geology study.Thanks for sharing this info.It should be interesting to many people.

This was very interesting to me guys. Thank you Mel Sabre52  and Jim, jamesp   

 I learn a lot for a dummy. That Uvalde material is such the bomb.            

[Fossilman]

Great reports! Love the Rio Grande material,so much variety.......A couple of or three friends on this site barter with me on a box or two of Texas goodies... I like it all...LOL

[Fossilman]

Here are the "Devils Toe Nails" we collect in Montana.......