Green River Fossils!

If you are a science geek then the prospect of digging up your own fossils has, at some point, probably excited you. The thrill and excitement of finding, seeing and touching something that hasn’t been seen for 50 million years is an incredible feeling.

While there are many different ways to find fossils, you can search in streams and oceans for shark teeth and bones, you can dig in the badlands for dinosaur bones, you can search the world for fossils. But if you’re like me, then extra time is not a resource you can come upon easily so here’s how I fuel my fossil hunting desires!

Southwest Wyoming is home to an area known as fossil lake, which is a part of the Green River Formation that consisted of 3 HUGE lakes that covered what is now Colorado, Utah and Wyoming.  Fossil lake has the richest deposit of freshwater fossils in the world! These fossils are found in the local limestone and are as easy to get to as walking up to a rock and picking it up. In and around Kemmerer Wyoming you can find a number of fossil quarries that, for a fee, will allow you to hunt fossils all day long. Some will even take you on night digs to help uncover pristine, museum quality fossils for the so called 18 inch layer (more on that later).

common fossil fish found in the green river formation
common fish found in the green river formation

But why limestone and not any other rocks?

To understand HOW to split it and WHY you’re splitting it, you need to know a little about how its formed. Limestone is a sedimentary rock formed by deposition of material (minerals, calcium carbonate, etc..) over time usually in bodies of water. As fish, birds, mammals, bugs, etc die, they fall to the bottom and are covered again by more sediment. Over time, the critters that are trapped can end up as fossils. All that being said, you can easily see the different layers of limestone when you look at it from the side. If you look close enough, you can see spaces that a chisel an fit into to separate the rock layers. Carefully splitting the layers can expose full beautiful fossil specimens!

Different Layers provide different quality of fossils.

Obviously over 50 million years, there are deeper layers of limestone than others in fossil lake. There are 2 layers we are really concerned about. The first layer is what is referred to as the 18 inch layer. The 18 inch layer produces some of the finest specimens in the world. Why? One word, Kerogen. Kerogen is derived from algae that have settled to create layers alternating with limestone. The Kerogen forms a very strong “glue” that holds the layers together. When the 18 inch layer is split, it will split along the weaker, non-kerogen, layers that are not as likely to hold fossils. The split limestone contains complete specimens that can be prepared with special tools to create incredibly detailed fossils.

The second layer is what is called the “split fish layer”. This layer of limestone does not contain kerogen so the limestone is weakest in the layers that do contain fossils. When you split this layer, its common to immediately expose fossils. This layer usually does not contain specimens detailed enough for scientific study because of damage from splitting but it’s a perfect layer for fossil collectors. This is the layer we will focus on.

Here’s a few tidbits about the limestone from the green river formation.

– 9 inches of limestone represents about 1 million years!

– Over millions of years, volcanoes erupted spewing large amounts of ash into the atmosphere. The ash layers will show up in the limestone as geologic markers. They are thicker than normal limestone layers and are called tuff layers.

– Volcanoes in what is now Yellowstone National park spewed ash clouds that settled in the lake. This is how they know that the sediment is approximately 50 million years old or early to mid Eocene.

– Organic layers are where you find the vast majority of fossils. These layers are stained different colors which allow visualization of the fossils in the different layers.

Digging for fossils at a quarry in Wyoming
Digging for fossils at a quarry in Wyoming
Mirror images of a fossil found after splitting limestone.
Mirror images of a fossil found after splitting limestone.

Because of the constant sediment in fossil lake, the fossils have been preserved in layers of limestone that are easily accessible to everyone.


The very best Limestone is from quarries around South West Wyoming in what’s known as Fossil Lake in the Green River Formation. Obviously it’s easy to get if you live within a days drive but for most of us, that’s not the case. Don’t worry we can supply you with anywhere from 10 – 30 LBS of quality limestone for your splitting pleasure DIRECTLY from the quarries in and around Kemmerer Wyoming. More on that at the end….

You also need:

– A hammer for splitting. A rock hammer is ideal, between 12-16 oz is fine. 20 oz hammers work well too but may be a little overkill.

– Chisel to separate the layers. The best is a dual beveled thin chisel to gently separate the thin layers of limestone without cracking them. The best chisels are specifically made for this purpose and can be found at You can use a regular chisel found at the hardware store but you need to be careful because they are much thicker.

– Gloves for protecting your digits. Not required but trust me, you will want some. Limestone is heavy with sharp edges and hammers hurt.

– Eye Protection. When chiseling anything, pieces fly off and eventually and inevitably hit your eye.

– Curiosity and Excitement! Splitting limestone for fossils is fun and rewarding. Seeing something that hasn’t been seen in 50 million years is quite a thrill!

Kids and adults alike love splitting Limestone and finding fossils. Its a true learning experience and it inspires kids to pursue interests other than xbox and playstation (although there’s nothing wrong with either). It’s nice to get your hands dirty and experience the world around you!

So lets get started!!

Some of the equipment you need to discover fossils in limestone.
Some of the equipment you need to discover fossils in limestone.

Get your limestone

Not just any limestone will do! You need fossil rich limestone which, as we have said before, is best from the quarries of southwest Wyoming. Do not fear! If you can’t come to the limestone, we can send the limestone to YOU! Just scroll down for instructions on ordering!

THIS is fossil rich limestone!
THIS is fossil rich limestone!

Third: Use chisel to separate the limestone layers

Thin chisels work best. You can easily identify the separate layers of limestone if you turn the rock on it’s side. You want to place the chisel directly in the space and GENTLY tap the end of the chisel with your hammer. As the chisel enters the limestone, you want to take care to not shatter the stone. As the chisel gets deeper in the limestone, you can start to gently push the layers apart.

Use a thin chisel to gently separate the limestone layers.
Use a thin chisel to gently separate the limestone layers.

Fourth: Bask in the AWE of witnessing something that hasn’t seen the light of day in 50 MILLION YEARS!

After separating the layers, you may or may not find a fossil. Sometimes you will find part of a fossil or you may find an entire well preserved specimen. Either way it goes, its an AMAZING feeling to touch something that hasn’t been seen in millions of years!

fossil specimen found in split limestone.  Hasn't seen the light of day in 50 MILLION YEARS!
fossil specimen found in split limestone.  50 MILLION YEARS old!



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