Pierre Shale Fossils

shell imprtint

I have long been wanting to explore the area known as Bacculite Mesa near Pueblo, Colorado searching for various fossils in the Pierre Shale deposits.  This site is on private land but the land owner does allow clubs to visit on planned trips.  This year I was able to make the field trip with the Canyon City and Lake George clubs.

The Western Interior Seaway had Colorado as the ocean floor around 70-80 million years ago.  This was before the mountains were formed and all over Colorado there are fossils contained in Pierre Shale deposits.  I have found pyrite and marcosite concretions in this general area coming out of the Pierre Shale.  This is a rare and premiere location for fossils from this era of our geologic history!

Spanish Peaks
Looking SW over Pueblo towards the Spanish Peaks from the Bacculite Mesa.
Dave and Pierre Shale formations
Thanks David for taking this picture of me and the Pierre Shale formations of Bacculite Mesa locality.

I carpooled with another fossil enthusiast David (thanks for the ride and company!) and we both had a great day and some amazing finds.  David suggested hitting the back side of the collecting area and we found some great fossils in that area; but limited bacculites which was mainly on a different face of the mesa.

Collecting area we were in. Photo courtesy of David Gillard.

I found the bacculite fossils pretty much in every zone of these hills including on top, especially in the small ravines and in wash outs below the hills.  I dug in a couple of spots that had quite a few rocks and fossils in the area, but didn’t find anything in-situ.

Various bacculites are common if you look through the alluvial slopes as they have weathered out of their host Pierre Shale and made their way down the hill.  These multicolored bacculites are 4-6 inches long.
Bacculite spine
This is a bacculite tail that can flex, it is interlocked like vertebrae.
Here is what bacculites looked like. Taken from http://www.bhigr.com/media/photos/rplca/bacculites_grand.jpg

I found a couple spots where there was calcite (?) crystals in the fossils, like you see in the clams from Florida or septarian nodules.  These were eroding out of harder rock and not the Pierre Shale, I’m assuming some kind of reef as the rock was full of imprints of fossil clams, shells and ammonites.

shell imprtint
Shell imprint in shale.
Nymphalucina occidentalis
Small clam Nymphalucina occidentalis
Weathered bacculite with shale matrix attached.
Unknown concretion, love the red/yellow/orange staining and patterns!
Little conglomerate ball, about an inch.
I love this triangle shell in a partial cube!
Calcite cluster, about 3 inches.
Veins of calcite mineralization
bacculite head
I believe this is the head of a small bacculite–which you can see protruding from the left side.


More calcite (?) crystallization


Bacculite with some of the iridescent patterns
Fossil clam with calcite mineralization
Some of the larger calcite (or barite?) crystals. These were beautiful amber color and translucent and in some spots gemmy.  Up to an inch.
Prickly Pear Cactus were in bloom!

David found this bacculite head right away; preserved in matrix!
David’s ammonite fossil.
Cool color and design on this shale rock; about 4 inches.
Various clams and shells. Many have calcite cores.


    1. Craig. First, thank you for the kind words regarding my blog diary! I appreciate knowing that other folks (other than myself) are visiting and enjoying–that will keep me motivated to do more! And thank you sooo much for the link! Wow, this is a detailed and relevant article. I really appreciate the information!

  1. Would love to hike with you and learn to find gems live in colorado springs and i can show where to find turtle sqiud and a million clam shells. Thanks.hope to from you.

  2. I have a property near brush hollow in Penrose Colorado. Its only minutes away from Pueblo west. I have always been interested in, and taken with paleontology and archeology alike but have never had the chance to persue anything like that in any way. I DO know that my 40 acre property here is littered with fossils and would lie to speak with you about it. I would be more than happy to let you come on property any time and see what you can find. Is there a way we could private message each other to discuss this all further?

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