Franklin Creek State Natural Area

Franklin Creek State Natural Area spans 922 acres in northwest Illinois, including a 198-acre Illinois Nature Preserve dedicated in 1970. The site features high limestone and sandstone bluffs, a spring-fed creek, and a wide range of plant and animal life supported by diverse terrain and soils.

Natural Features

Franklin Creek flows through a deep valley carved into ancient bedrock, creating a sheltered environment where forests, prairies, and cliff communities thrive. This landscape supports a rich mix of flora and fauna and serves as an important habitat for both resident and migratory species.

The preserve represents one of the earliest protected natural areas in Illinois and remains the foundation of the larger state natural area.

Geology

The geology of Franklin Creek is especially notable because the valley exposes three distinct layers of rock formed during the Ordovician period more than 450 million years ago.

  • New Richmond Sandstone
    The oldest layer, about 485 million years old, forms the base of the gorge. It is a soft sandstone with traces of dolomite and chert.
  • Shakopee Dolomite
    Slightly younger, this layer consists primarily of fine-grained dolomite with some sandstone, shale, and siltstone. Fossils are commonly found here.
  • St. Peter Sandstone
    The youngest layer, about 458 to 453 million years old, is composed of very pure quartz sand. It has historically been valued for glassmaking and contains few fossils.

 

Above these rock layers lie glacial deposits from the Wisconsin glaciation and a surface layer of loess soil that supports today’s vegetation.

Fossils

The rocks at Franklin Creek formed in an ancient shallow sea, so fossils here are marine in origin.

Common finds include:

  • Marine snails and shells
  • Trilobites, extinct arthropods with segmented exoskeletons
  • Orthocones, cone-shaped relatives of modern squid
  • Brachiopods and bivalves such as clams and scallops
  • Scolecodonts, fossilized jaws of ancient marine worms
  • Trace fossils such as burrows and movement marks

 

Collecting fossils is not allowed on state land.

There are several places to check out if you’re interested in geology. These include:

  • Whipple’s Cave, as mentioned above shows all three rock formations known at FCSNA.
  • Lover’s Leap is a massive bluff overlooking the creek. Nearby, you’ll find chunks of rock that have fallen from the cliffs above, revealing cross-bedding.
  • By Monday’s Bridge there is another series of outcrops overlooking the creek, supporting wildflowers such as Penstemon, ​as well as rarities such as Canada yew and several types of ferns.
  • The old Quarry contains several interesting quirks of geology, including paper thin sheets of sandstone.
  • The Hausen-Knox Shelter near the Quarry has several boulders lining the parking lot, where you can see chert (microscopic quartz crystals) and dendrites.
  • There is a wall by the Grist Mill parking lot in which you can see fossils.
Geology Brochure

Vegetation

Plant communities vary based on soil, moisture, and elevation.

  • Bottomland Forests
    Found along the creek, dominated by silver maple and hackberry, with slippery elm and Kentucky coffeetree.
  • Mesic Upland Forests
    Located in ravines with sugar maple, basswood, and understory species like pawpaw.
  • Dry-Mesic Forests
    Found on higher ground with oak species, shagbark hickory, and hop hornbeam.
  • Prairie Remnants
    Small glacial drift hill prairies support Indian grass, tall dropseed, and other native prairie plants.
  • Cliff Communities
    Undisturbed rock outcrops support species such as Canada yew, bladdernut, shooting star, and several ferns.

 

Spring is an especially popular time to visit, when wildflowers like bluebells blanket the forest floor.

Plant List
Trees Scavenger Hunt

Wildlife

The natural area provides habitat for a wide variety of wildlife.

  • Birds
    Woodpeckers, flycatchers, thrushes, vireos, warblers, and herons are commonly observed. The area is also an important migration stop.
  • Mammals
    Raccoons, chipmunks, squirrels, beavers, deer, foxes, and weasels inhabit the area.
  • Reptiles and Amphibians
    Toads, frogs, turtles, and water snakes may be seen near the creek.
  • Fish
    Franklin Creek supports species such as smallmouth bass, channel catfish, carp, rock bass, and redhorse.
FCSNA Animal Database
Bird Scavenger Hunt

Flora

Within Franklin Creek State Natural Area there are several high quality plant communities. Here you can view the different blooms throughout the growing season. If you have pictures from the area that you would like to submit please contact us for picture donations. FCCA is committed to the preservation and restoration of our natural areas. To help us reach our goals, please consider making a donation of time on our stewardship days or a financial donation.

Flora List

Invasive Species

Invasive species are those that are not from the area which they are growing and have the ability to outcompete native flora and fauna for resources leaving a degraded and less diverse habitat for native flora and fauna, causing the decline in those species.

  • Bird’s-Foot Trefoil (Lotus corniculatus)
  • Orange Daylily (Hemerocallis fulva​)
  • Wild Parsnip (Pastinaca sativa)
  • Yellow Sweet Clover (Melilotus officinalis)
  • Dame’s Rocket (Hesperis matronalis​)
  • ​White Sweet Clover (Meliotus alba)
  • Crown Vetch (Securigera varia)
  • Amur Honeysuckle (Lonicera maackii)
  • Teasel (Dipsacus fullonum)
  • Garlic Mustard (Alliaria petiolata)
Tree Thinning

Trails & Recreation

Hiking Trails

More than 4.5 miles of marked trails wind through the natural area.

  • Mill Springs Trail
    A paved, accessible trail leading to Mill Spring.
  • Pioneer Pass Trail
    A scenic route with creek crossings.
  • Seasons of Change Trail
    Interprets how habitats change throughout the year.
  • Husar Memorial Trail
    Features nature quotes, a sculpture, and historic structures.
  • Storybook Trail
    A family-friendly trail with illustrated story panels.
FCSNA Trail Map

Equestrian Use

About 12 miles of equestrian trails are maintained with support from local riding organizations. Facilities include a shelter, restrooms, water, and an outdoor show area.

Winter Activities

  • Cross-country skiing is available on select trails after hunting season.
  • Snowmobiling is permitted when conditions allow with adequate snowfall.

Fishing

Fishing is allowed on state-owned sections of Franklin Creek. Anglers may catch smallmouth bass, catfish, carp, and other species. Check current consumption advisories before eating fish.

Picnicking

Multiple picnic areas and shelters are available, some with electricity, grills, water, and restrooms. Several shelters can be reserved through the state reservation system.

Hunting

Managed hunting programs include deer reduction efforts and seasonal turkey hunting in designated areas. Contact the site office for current regulations.