Fort Union Formation Clinker Fossil Earthcache EarthCache

PLEASE do not park on the road. There is one parking spot available at N46 24.345 W105 39.202 on the east side of the road. This site would be difficult for RVs and Truckers, though smaller SUVs/pickups hauling short trailers would be just fine.

The walk to the roadcut is only about 300’. Please use wisdom when crossing the street to the west side of the road. The roadcut geology in question itself is across a shallow gully and thus is well away from the road.

The terrain is listed as a “3” because of the steepness of the hillside/roadcut. You will need to do some scrambling up the hillside, so be sure you are wearing a decent pair of shoes/boots!

The Tertiary Fort Union Formation is predominate in eastern Montana. The Fort Union Formation is a geologic unit containing sandstones, shales, and coal beds in Wyoming, Montana, and parts of adjacent states. The Fort Union is mostly of Paleocene age and represents a time of extensive swamps as well as rivers and lakes that assisted in laying down sedimentary deposits throughout the region. The rocks are more sandy in southwestern Wyoming and more coal-bearing in northeast Wyoming and southeast Montana, reflecting a general change from rivers and lakes in the west to swamps in the east, but all three environments were present at various times in most locations. In most area roadcuts, one can see the thin-bedded sandstone and hard shale exposed to view. The sandstone has taken on a “harder” baked form than one is used to seeing, because of naturally occurring fires from lignite coal underground. (Lignite coal is a low-grade coal that is 25-35% coal and up to 60% water. It has the tendency to spontaneously combust, yet is considered valuable because it is easily converted into petroleum.) This baking action has turned the sandstone into a much finer and harder substance that is referred to by locals as “clinker” or scoria, though technically, these terms refer to sandstone that has been altered by volcanic action. In reality, the resulting alteration is porcelanite.

Logging Requirements: Send the answers to #1-#3 to me through my geocaching profile.(Since the advent of the "new" Message the Owner feature, I prefer messages through that venue(

1. Examine the two layers viewable in this roadcut. Describe the differences/similarities in color, plane (what shape is it when it is broken or in pieces), and texture.
2. Scramble up to the top layer, examining the fossils present throughout the formation. What differences do you see in what fossils exist in the two distinct layers?
3. Optional: If you are able to find any fossils in this roadcut, measure the largest fossil found, please include measurements of the largest fossils found in your email to my profile.
4. Take a picture of yourself and your GPS with the roadcut plainly visible behind you. DO NOT show off pieces of rock that might give aw(Per current gc.com guidelines, photos are no longer allowed to be required. HOWEVER they are encouraged, since they can help clarify that you have visited the location if your other logging requirement answers are vague). ay the answers to other logging requirements. Please post your picture simultaneously with your log, otherwise you endanger your log being deleted.

Note: As of 2009, collecting a reasonable amount of fossils from this roadcut was considered possible by the writers of the FalconGuide Rockhounding book. However, collecting permissions and guidelines change frequently as ownership and state laws change. If you choose to collect from this site, be sure you are aware of state guidelines BEFORE you collect. Also, remember that federal guidelines prohibit the collection of any vertebrate fossils. In this formation, you should not be able to see any vertebrates!

Resources:

• Wikipedia “Fort Union Formation” http://en.wikipedia.org/wiki/Fort_Union_Formation
• Wikipedia “Lignite Coal” http://en.wikipedia.org/wiki/Lignite_coal
• Rockhounding Montana. Montana Hodges. A FalconGuide.
• National Park Service Information Panels, Theodore Roosevelt National Park.