Guidebook—Geology of Northeastern Kansas

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color photo of participants with outcrop and overpass in background

At the fossil stop.

Stop 4--Fossils at the K-4 and U.S. 24 Interchange

Please note: The Kansas Department of Transportation has closed this site to the public.

The new interchange at the junction of K-4 and U.S. Highway 24 is an easy place to see and collect invertebrate fossils. Fossils are the ancient remains or evidence of once-living plants and animals, and invertebrates are animals without backbones. In Kansas, invertebrate fossils are much more common than vertebrate fossils. Even so, they represent only a tiny sampling of the animals that once inhabited this part of the earth, most of which lived and died leaving no visible trace.

color photo of hand holding rock with spiral fossil

Close-up of a gastropod fossil collected at this site.

The fossils here give an idea of the variety of animals that lived in the Pennsylvanian seas, roughly 300 million years ago. Among the fossils found at this site are brachiopods, bryozoans, crinoids, gastropods (snails), bivalves (oysters, clams, scallops), and trilobites. The less familiar of these are described in more detail below.

Two rock units here, the Holt Shale and Coal Creek Limestone Members of the Topeka Limestone, are particularly fossiliferous. The Holt Shale Member is a dark-gray, layered siltstone, about 2 feet thick. Fossils of brachiopods and bryozoans (see description below) are common in this member. The Coal Creek Limestone Member, which sits directly above the Holt Shale Member, is a light-gray or olive, silty limestone, about four feet thick (see stratigraphic column).

color photo

This limestone is covered with fossils, mostly fragments of crinoids and bryozoans, which are common at this site. The rock also contains the tail segment of a trilobite (just above and to the right of the penny), a relatively rare fossil in Kansas.

In addition to the fossils at this site, you can see coal, exposed at the surface in the Calhoun Shale, the formation just below the Topeka Limestone. Pyritized wood is also found in the same vicinity as the coal, just above the coal layer in the Calhoun Shale. Learn more about coal in Kansas.

Bryozoans are some of the most abundant fossils in sedimentary rocks, and they are also widespread today, both in marine and freshwater environments. Bryozoans are small animals (just large enough to be seen with the naked eye) that live exclusively in colonies. Bryozoans are sometimes called moss animals--the name comes from two Greek words, bryon (moss) and zoon (animal)--because some bryozoans form colonies of bushy tufts that resemble mosses. Bryozoan colonies can also resemble colonies of some corals. Like corals, most bryozoans secrete external skeletons made of calcium carbonate, but unlike corals, bryozoans generally don't build reefs. Each bryozoan colony starts out with a single individual, called a zooid. Each zooid is essentially cylindrical and has a ring of tentacles that it uses to feed, drawing tiny plants and animals towards its mouth. As the first zooid begins feeding, it buds to form additional zooids, each of which has its own feeding tentacles. The new zooids also bud, forming the colony. Large colonies may consist of hundreds of thousands or even millions of zooids. Fossil bryozoan colonies come in a variety of shapes. Some bryozoans built colonies that grew from the seafloor in branching structures; these fossils look like something like twigs. Other species erected netlike frameworks, while still other spread like a crust on shells, rocks, plants, and even other bryozoan colonies. All of these types of bryozoan colonies can be seen at this site. Learn more about fossil bryozoans in Kansas.

Brachiopods are marine animals that secrete a shell consisting of two parts called valves. Their fossils are common in the Pennsylvanian and Permian limestones of eastern Kansas. Brachiopods have an extensive fossil record. They first appear in rocks dating back to the early part of the Cambrian Period, about 545 million years ago, and were extremely abundant until the end of the Permian Period, about 250 million years ago, when they were decimated in the mass extinction that killed more than 90 percent of all living species and was the largest of all extinction events (larger than the major extinction at the end of the Cretaceous that killed off the dinosaurs). A distinctive feature of all brachiopods is that their valves are bilaterally symmetrical--that is, the right half is a mirror image of the left half. (Humans are also bilaterally symmetrical.) The bilateral symmetry of the individual valves differentiates brachiopods from clams and other bivalved mollusks, with which they are sometimes confused. Unlike brachiopods, clam valves are not bilaterally symmetrical; instead, the right and left valves are mirror images of each other. Brachiopod shells come in a variety of shapes and sizes. The outer surface of the valves may be marked by concentric wrinkles or radial ribs. Some brachiopods have prominent spines, but these are generally broken off and incorporated separately in the sediment. Learn more about fossil brachiopods in Kansas.

Fossil clams are generally easy to recognize because they look a lot like the shells scattered along modern seashores. Clams and their relatives (oysters, scallops, mussels) are often called bivalves (or bivalved mollusks) because their shell is composed of two parts called valves. Like their living relatives, fossil bivalves come in many different shapes and sizes. Typically the right and left valves are symmetrical (in contrast to the bilateral symmetry of individual brachiopod valves), though some bivalves, such as oysters, have valves that are not symmetrical. In western Kansas, fossil clams found in younger rocks from the Cretaceous Period are even more common. Some of these--the inoceramid clams--are huge, as much as 6 feet in diameter. Learn more about fossil bivalves in Kansas.

Crinoids are another animal that lived in the Pennsylvanian seas. Because they resemble plants, with feathery arms set atop a long stem, crinoids are sometimes called sea lilies. But they are definitely animals--relatives of starfish, sand dollars, and sea urchins. Crinoids appeared in the fossil record about 500 million years ago and still inhabit the world's oceans. Well-preserved fossils of entire crinoids have been found in the chalk of western Kansas (and are on display in museums around the country). Usually, people find only pieces of the crinoid stem, which are shaped like little buttons and were used by Native Americans as beads. At this site, you might also find the crinoid calyx, the cup-like part that sat on top of the stem. Learn more about fossil crinoids in Kansas.

Trilobites are an extinct group of arthropods, relatives of insects, spiders, ticks, crabs, shrimp, lobsters, and numerous other organisms. They were exclusively marine organisms. Trilobites first appear in the fossil record in rocks deposited during the Lower Cambrian, about 540 million years ago. Although they were extremely abundant during their first 100 million years or so, by the Pennsylvanian and Permian Periods (when the surface rocks in eastern Kansas were deposited), trilobites were much less dominant. They became extinct, along with many other species, at the end of the Permian. The bodies of trilobites, like insects, have three parts: the head (or cephalon), the thorax, and the tail (or pygidium). Leg-like appendages attached to all three parts, but these are rarely preserved. Because of this, and the fact that trilobites have no living counterpart, paleontologists are hesitant to speculate about how trilobites lived. Trilobite pygidia are sometimes found at this site. Learn more about trilobite fossils in Kansas.

Directions to Stop 4

To get to the new interchange at the junction of K-4 and U.S.-24 northeast of Topeka, approach the interchange from the south on K-4. As you are driving north, pull off to the right side of the road immediately past the first exit ramp, but before you come to the overpass. If the ground is dry, there is a dirt road that will get you safely off the highway. Park near the underpass. The rocks exposed immediately to the east are easily accessed by walking north down to the end of the exposure and then walking back on the flat bench that has been excavated into the cut. The fossils occur in the 6 or 7 feet of rock above this bench.

From Stop 4 to KGS

From stop 4, the route continues east on U.S. 24 to Perry, Kansas, mostly travelling in the Kansas River floodplain. The route heads south from Perry and crosses the Kansas River at Lecompton. Here, on the south bank of the Kansas River, just above river level, members of the Oread Limestone are visible. A short distance upstream the Oread disappears from view, dipping below the alluvium of the Kansas River. The route joins U.S. 40, just below the escarpment of the Deer Creek Limestone, and heads east to Lawrence, crossing the Lecompton cuesta and returning to the Oread Limestone and the Kansas Geological Survey.


Tarbuck, Edward J., and Lutgens, Frederick K., 2000, Earth Science (9th Edition): Upper Saddle River, New Jersey, Prentice Hall, 672 p.

Wicander, R., and Monroe, J. S., 1989, Historical Geology--Evolution of the Earth and Life through Time: St. Paul, Minnesota, West Publishing Company, 578 p.

Zeller, Doris, ed., 1968, The Stratigraphic Succession in Kansas: Kansas Geological Survey, Bulletin 189, 81 p.

This guidebook is also available in print form as Kansas Geological Survey, Open-file Report 2000-55, from KGS Publications Sales office, 785-864-3965.

Unless noted otherwise, illustrations by Jennifer Sims, Kansas Geological Survey; photographs by John Charlton, Kansas Geological Survey. Text by Jim McCauley, Liz Brosius, Rex Buchanan, and Bob Sawin, Kansas Geological Survey.

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