Living on the Reef: The Whitewood Formation

🚙 US-14A Mileage11.3 GPS Coordinates N 44.22.418 W 103.55.238 4,857 ft.

Living on the Reef Update2.pdf

In Ordovician Time it formed

With fossils filled galore

A dolomitic rock with tales

Of corals, clams and more

Field Exploration

Climate change? Yes indeed – the one thing that never rests! As we roll back the clock of time you'll be entering an Era of tropical climates where we'll place you on the shores of the Ordovician Sea – a world teaming with ocean creatures and coral reefs. Our exploration will conclude with a search for ancient invertebrate fossils and a giant coral specimen that you simply must see!

This pdf Lesson Guide contains the specific directions for reaching our featured site as well as a detailed explanation of its geologic story. Mileage and coordinates are provided in each document and roadmaps and other learning aids can be found at the Lesson Resources link in the sidebar menu. The document is most useful if taken with you to the lesson site. Exercise extreme caution at the lesson site and along roadways.

Are you ready. . . . Let's Go! S. V. Fogarty & W. R. Stevens

*Mileage starts at the intersection Colorado Bvd. and US 14A near Spearfish.

Iron Creek Trail

Whitewood Dolomite

Iron Creek

Parking is available behind and to the right of the guardrail just prior to reaching the Iron Creek sign. From here it's only a short walk down the trail to the lesson site in Iron Creek Canyon.

Fat Bike Trail Sign

You'll know you're on the correct rail when you see the Big Hills Fat Bike Trail Sign. It is truly the trail to Iron Creek but it also serves as a leg of a larger Big Hill Fat Bike trail complex. The lesson site includes the rocky outcroppings and loose rubble along the right side of the trail as well as one interesting area closer to the creek bed on the left. See map below for details. The Whitewood Formation outcrops in the lower cliffs along the trail. Be sure to print out the pdf lesson for directions to an amazing fossil coral.

The Iron Creek hiking trail follows the creek upstream to Iron Creek Lake and traverses the Whitewood Dolomite (Dolostone) along its course. You'll see this great outcrop about 125 yards from the trail sign. As seen in this picture the Whitewood tends to be orange-brown in color and can be most easily observed in the lower canyon walls along the right side of the trail. The younger Pahasapa Limestone can be seen in the upper cliffs and tends to be a bit lighter in color and not quite as "blocky" in texture. The Englewood Formation lies directly between these two formations but is not visible in this photo. The Whitewood is Ordovician in age and is best know for it's rich invertebrate fossil assemblage. See the Stratigraphic Column below for the position of the Whitewood Dolomite within the stack of rock layers exposed here in Spearfish Canyon.

Note the position of the Ordovician Whitewood Formation in the diagram above. The Whitewood Formation is noted for it's wide variety of marine, invertebrate fossils. Age and thickness are approximates.

Common Fossils of the Mississippian.pdf

Mississippian Fossil Guide (Print)

Common Fossils of the Ordovician.pdf

Ordovician Fossil Guide (Print)

These fossil guides will be useful in identifying specimens you may find in the rocky rubble along the base of the canyon walls. You can print out the guides at either the Lesson Resources page or from here directly. They will be helpful if you decide to engage in some fossil hunting.

Ordovician Tabulate Coral in Whitewood Dolomite. The location of this specimen is shown in the map below but for more assistance a photographic depiction of it location is available in the pdf lesson posted at the top of this page.

Chert nodules are common in limestone & dolomite.

A conglomeration of invertebrate fossils.

Dolomite contains numerous invertebrate fossils.

Rocky Rubble

As the Whitewood Dolomite weathers away, fragments fall from the adjacent cliffs and accumulate along its base. These piles of rocky rubble are good places to look for fossils and other geologic oddities. The more fragments you pick up and examine the better your chances of finding something of interest. Just a few examples can be seen in the photo above. Some fragments fall from the younger formations above the Whitewood as well so one can expect some Mississippian fossils in the mix. Because the Ordovician and Mississippian fossils are numerous you may find the fossil identification guides posted above to be quite useful.

FOSSIL LOCATION MAP

The fossil Tabulate Coral can be found preserved in one of the large boulders lying between the trail-bed and Iron Creek. DO NOT cross over to the south side of the creek. The fossil is near the west end of the rubble and not too far away from a tree. Take care not to damage the fossil but be sure to take some pictures. Good luck! Print out and read the provided lesson for more details.

Be sure to download our Onsite Geology Lesson PDF posted above for a detailed geologic investigation of this site.

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