Friends of Nachusa Grasslands
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Stop 3 — St. Peter Sandstone

​The bluffs at Tellabs Savanna offer a stunning topographical relief at Nachusa Grasslands, besides providing a scenic setting with majestic oak trees looming above the colorful flowers of the sand prairie. These outcrops are St. Peter sandstone, sedimentary rocks that were deposited in near–shore or marine environments during the Ordovician period approximately 450 million years ago. At that time, northern Illinois was situated on the continent of Laurentia, in the tropics south of the equator.

​What is sandstone?
Sandstone is a soft rock made of a hard mineral. You can often crumble sandstone with your bare hand, but if you look at the sand with a hand lens, you see frosted, well–rounded grains of a mineral, quartz, that rates 7 out of 10 on the hardness scale. Because the grains are not very well cemented together, it is very susceptible to erosion by wind, water and biological activity, resulting in the sculpted shapes you see here.
 
The St. Peter Sandstone, being extremely pure quartz, is used for the manufacture of glass, filter and molding sand, as an abrasive, and in the hydrofracturing of oil and gas wells.
 
Journey off the trail to a sandstone outcropping and find . . .
  • The sediment layers in the rocks. See the parallel stripes?
  • Lichen growing on the rocks. Lichen is a plant, which results from the partnership between a fungus and algae.
  • Plants growing in cracks between the rocks. The plant roots will eventually split the rocks apart.
  • Insects​
​St. Peter sandstone forms the exposed bedrock everywhere on Nachusa, with the exception of isolated exposures of dolomite (a type of limestone) at the Carpenter and Hook Larson units, and the bluffs along Babbling Brook in the Orland tract (seen along the Big Jump trail). The St. Peter sandstone forms the knobs on the Hamill–Winter Prairie and the ledges at Shabbona Savanna. It makes up the “castle rocks” that overlook Rock River at the state park near Oregon and the ‘starved rock” at the state park near Ottawa.
 
CAUTION! Danger of falling. Stay well back from the cliff edges and do not climb on the rock faces, as the sandstone is very soft and can easily crumble under your weight. Feel free to explore the rock face all you like from the bottom, always being aware of the danger of falling rocks or other objects. 

Stop 4 — Sandstone Bluff Planting

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8772 S. Lowden Road  (mailing address)            
2075 Lowden Road (Visitor Center)           
Franklin Grove, IL 61031

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  • Home
  • About Friends
    • Mission, Leadership, Objectives, and Financials
    • Friends Annual Meeting 2025
    • Endowments
    • Heritage Heroes Initiative
    • Friends Annual Reports
    • Newsletters >
      • PrairiE–Update (email)
      • A Prairie Calling (print and digital)
    • Commenting Policy
  • Plan Your Visit
    • Hours & Parking
    • Directions and Map
    • Visitor Center
    • Pet Policy
    • Public Bison Tours
    • Bison Viewing
    • Hiking >
      • Hiking Guidelines
      • Hiking Destinations
      • Guided Hikes
      • Stone Barn Savanna Tour
      • Visitor Center Trail
      • Scavenger Hunt
    • Autumn on the Prairie >
      • Yearly Festival
    • What's In Bloom?
    • Exploring Nachusa Grasslands on Your Own
    • Things to Do
    • Places to Eat and Stay
    • Local Sites to Visit and Explore
  • Donate
  • Calendar
  • Volunteer
    • Volunteer Opportunities
    • Thursday and Saturday Workdays >
      • Workday Signup
      • Workdays – November to February
      • Volunteer Workday Safety Protocols
      • Leader Workday Safety Protocols
      • Steward Workday Tips
    • Workday Email List
    • Volunteer Recognition
    • Docents
  • Stewardship
    • Nachusa Stewardship
    • Restorations
    • Planting Histories >
      • Stewardship Unit Planting Histories
      • Planting Histories in Chronological Order
    • Weed Reports
    • Native plant resources
    • Volunteer Stewards
    • Groups and Committees
    • Available Units
    • Controlled Burns
    • Prescribed Fire Recruitment
    • Restoration Publications
    • Stewardship Resources >
      • Seed Collection Guides
      • Invasive Plant Management
      • Invasive Identification
      • Monitoring
      • Resource Links
  • Science
    • Science at Nachusa Grasslands
    • Science Symposium 2025
    • 2025 Science Symposium Abstracts
    • Science Grants >
      • Science Grants 2025
      • Science Grants 2021 to 2024 >
        • Science Grants 2024
        • Science Grants 2023
        • Science Grants 2022
        • Science Grants 2021
      • Science Grants 2016 to 2020 >
        • Science Grants 2020
        • Science Grants 2019
        • Science Grants 2018
        • Science Grants 2017
        • Science Grants 2016
      • Science Grants 2011 to 2015 >
        • Science Grants 2015
        • Science Grants 2014
        • Science Grants 2013/2012/2011
    • Potential Research Topics
    • Scientific Publications
    • Anderson Science Award
    • Science Videos
    • Become a Community Scientist >
      • About Community Scientists
      • Butterfly Monitoring
      • Calling Frog Monitoring
      • Dragonflies & Damselflies
      • RiverWatch
  • About Nachusa
    • General Info
    • Nachusa Staff
    • Prairie Smoke Annual Reports
    • Plant Inventory >
      • Common Names
      • Genus Species
    • Animal Inventory >
      • Amphibians
      • Birds
      • Bison Bison >
        • Bison
        • Bison Babies Broadcast Videos
      • Fish
      • Insects
      • Mammals
      • Other Arthropods
      • Reptiles
    • History
    • Jobs
    • Hunting
    • Geology >
      • Geology Part 1
      • Geology Part 2
      • Geology Part 3
    • Websites of Interest
  • Teacher Resources
    • K-2nd grades
    • 3rd-5th grades
    • 6th-8th grades
    • High School
  • BLOG AND MEDIA
    • Nachusa Blog
    • In The News
    • Photo Gallery >
      • Spring Photos
      • Summer Photos
      • Autumn Photos
      • Winter Photos
    • Videos
  • Contact Us / FAQs