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Petrified Blue Forest

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I had the opportunity to cruise around Wyoming, Colorado, and Utah on my own  for 5 days The first day of my fossil hunting excursion was to be spent at the Petrified Blue Forest site in Western Wyoming. Having been there before, I knew fragments of wood abound, many carrying the blue agate on it. But I was determined to find a “large” log this trip. I had researched how to up my odds and stopped at a hardware store the night before and purchased a shovel as step one. So early that morning, I found myself looking out at the vastness of this “forest” thinking where to start.






That is when this antelope startled me. After a short stare down both the antelope and I were on our merry way.




Soon after stepping out of my vehicle to scout around, I began finding many small pieces of petrified wood with the characteristic blue agate that everyone is after.




Here is a piece of wood next to a skull that I do not recognize. Any thoughts about what animal this was?




 After an hour, and not finding anything substantial, I jumped back into the car and followed an obscure path that led me to the top of a hill. From up here, one can appreciate the vastness of the region.




Looking around told me that petrified wood existed even up here. So out came the shovel again. The ground is made up of a loosely broken sedimentary like rock that can be shoveled with some (much) difficulty. As I dug, my eyes were intently focused on the hole created looking for a hint of an algae fossil that has a very distinct look to it. Why look for algae???? Because within the algal mat is where the wood lies! Finally, after many digs, some significant algae appeared in my hole. Here is a picture of it as found and the debris surrounding it removed. A piece of the top layer of algae is removed, exposing the wood inside.






Unfortunately, when I tried to wedge the log out of its hiding place it split in two, leaving this piece in tact and the other piece in a crumbled mess.






Thank goodness I had purchased a small container of acetone at the store and I immediately added it to the Paraloid  B 72 crystals I had brought with me from Minnesota. This stabilized the intact piece fairly well, though I could have used many more resin crystals than what I packed. 


The Blue Forest wood was deposited into a fresh water, algae filled, shallow lake that was full of silica. Soon after the fresh wood was deposited in the water, algae formed a thick crust around it. Here is a small branch showing the layering of algae.




The wood with time shrunk, providing space for the silica rich water to do its thing!!!! In addition to the mineral deposits, this wood has exquisite preservation due to the algae blanket protecting it from the elements. Here is a piece that shows the boring holes by insects as fresh as if they were made today.




Now some of my specimens brought home.  DSC_0182-001.thumb.JPG.5d0f0cda892b9a7eca72ae841a05d0b6.JPG


 Unfortunately, the specimens found on top of the Butte contained mostly yellow calcite crystals. Next time I will stay down below and hope for much bluer specimens.





























Here is a branch that was completely mineralized!!




















Edited by minnbuckeye
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Great report and photos, Mike.:)

Some f those pieces are very beautiful. 

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Great trip report Mike! What is the age of the wood? It reminds me of some of the pieces I find around here, just there's less beautiful agate here.

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@Top Trilo, I think this is correct.


National Geologic Map Database
Map showing publication footprint
    • Laney shale member

Schultz, A.R., 1920, Oil possibilities in and around Baxter basin, in the Rock Springs uplift, Sweetwater County, Wyoming: U.S. Geological Survey Bulletin, 702, 107 p.


Named as the third member from base (of four members) of the Green River formation for exposures along Laney Rim on the northwest edge of the Washakie basin, T18N, R97W, Sweetwater Co, WY in the Greater Green River basin. Extends east (geologic map) into Carbon Co, WY and south into Moffat Co, CO, also in the Greater Green River basin. No type locality designated. Also called the upper oil shale of the Green River. Unconformably overlies the Cathedral Bluffs red beds member (new) of the Green River. Unconformably underlies the plant beds and Tower sandstone of Powell. Consists of white and green fissile shale, limestone, and sandstone, and some dark bituminous shale. Ranges from 0-950 ft thick. One measured section 700 ft thick described at Lookout Mountain, WY, and another 850 ft thick described at T10N, R96W, that extends from the Snake River to the top of Sunny Point, Moffat Co. Stratigraphic chart. Of Eocene age.

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Congrats onthe great looking wood.


My understanding is that a lot of the popular (rock)hunting areas that require digging are pockmarked with holes that hadn't been filled in. I only see possible holes on the picture of your vehicle. Had you dug those or were they there?


(While I haven't been to digging sites, it seems that most of the videos I see when people go to these sites show previously excavated pits.)


I'm also a bit surprised that you got by with a shovel. I thought I had read that people who hunt that blue wood covered/encased by algae usually took along pick-axes etc., unless I'm thinking of a totally different site. 

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Nice report.  More tales from your fun trip.  Yes, the blue forest is eocene in age; possibly part of the laney shale member of the green river fm, which overlays the bridger fm at the blue forest.  (I just spent a few days collecting a small croc skull there in the bridger fm.  Blm land, blm permit, for work).

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Really cool site and nice report! Beautiful specimens!


That skull is some kind of rabbit or jackrabbit. Apparently there are seven different Lagomorph species that occur in Wyoming. You could narrow it down by further by habitat and range...




What is the story with this preserved algal mat? Is it known what species are involved? There must be some published descriptions somewhere(?). 

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Great trip report and finds, I really love the scenery out there.

Edited by Nimravis
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On 8/30/2022 at 9:58 PM, Houdek said:

are pockmarked with holes that hadn't been filled in


 @Houdek, Yes there is definite evidence of human activity. Unfilled holes are frequently encountered. I am surprised the antelope can survive out there without breaking a leg. And yes, a pick would be very helpful to have, but when traveling by plane, it is difficult to justify bringing it along!! I left my shovel at a construction site before going to the airport in hopes it may get more uses than just mine!!

On 8/31/2022 at 5:20 AM, karstic said:

Is it known what species are involved?


I have never seen a specific species of algae mentioned but research articles may contain the info you are looking for.

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I'm not a wood guy but after this very very interesting report, maybe I should start.  Very good report and some really good pics. 



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On our second trip to WY to go "fishing" in the Green River Formation the guide (I think I remember his name being Robert, not that it matters much). we used to take us to the fish quarries took us out to the Blue Forest. We didn't know about it on our first trip and built-in a little extra time on the second outing. The month before, one of the customers went out with him and the found a huge trunk with excellent color. He was traveling back home by plane and only wanted a smaller chunk which they sawed off with a slab saw. The rock shop Robert worked at kept the rest of the trunk and made many more beautiful slabs out of their find.


I worked for probably 30 minutes trying to dig through the "concrete" that was the matrix where these logs may be found. The elevation of this site had this flat-lander winded enough that I decided it would be more useful to surface hunt in the remaining time we had. Rather than try for a big score I was happy with some nice rounds that were 4-5 inches in diameter and were nicely bluish-black inside with wonderful texture on the outside.


Would enjoy going back out there again some day and spending more time in the "forest" to see what we might turn up. Thanks for bringing back some pleasant memories.






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@digit If I am not mistaken, I think Bob was the owner of a rock shop in Kemmerer and he sold out to a lovely couple who only does night digs now.

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Sounds about right. I thing Bob worked with George who ran the rock shop in the basement of an antiques shop in the main square.






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