Earth Cache: Rockport State Recreation Area
Submitted by Chuck Schepke
Roscommon High School schepkec@rapsk12.net
Earth Cache Lesson
Natural resource deposits we get from the Earth are related to the geologic past and change that occurred in that area over time.
Starting Point: N 45.1997°, W 83.3949°
From Alpena, head north on US 23 till you come to Rockport Road. Next, travel east (make a right from
US 23) down Rockport Road for about 2.3 miles to the Rockport State Recreation Area sign entrance.
Source: Personal picture from
2014 MESTA
Conference
Rockport Quarry
Field Trip
Google Earth 2008-today much of the quarry is sporadically covered with sparse and scrubby vegetation.
Rockport State Recreation Area Cache Summary
Source
: http://www.ncrs.fs.fed.us/gla/geology/mi-bedrock.htm
Rockport State Recreation Area is located about 20 minutes north of Alpena, located along the Thunder
Bay shoreline of Lake Huron. This site use to be an operating limestone quarry that operated from 1913 to 1949. After quarry ceased operations in 1949, the last notable event that occurred in Rockport was the construction of caissons that anchored the Mackinac Bridge’s two pier towers. The caissons were built on barges that were then towed to the Straits and the quarry stockpiles provided also backfill for the caissons. Rockport as of today is a state recreational area and is well known for Devonian fossil collecting. Devonian fossils of Michigan are marine origin, consisting of brachiopods, crinoids, corals, bryzoans, trilobites, gastropods, fish, blastoids, and cephalopods. At this Devonian time period (359 to
416 million years ago), Michigan was located by the equator and the large coral-stromatoporoid reefs and smaller bioherms (ancient organic reef of mound like forms built by a variety of marine
invertebrates) dominated. These reefs grew in clear, shallow, warm seas during the time of deposition of limestone. Calcium carbonate which organically or chemically precipitates out into limestone was a natural resource used to build these reefs and deposits, which we mine now to build our communities

infrastructures. Travel back in time in Michigan’s past back to the Middle of the Devonian Period over
350 million years ago, that is what a visit to the Rockport Earth cache will do for you. See references 2 and 3 for a visual guide for the various types of fossils.
U of M museum of Natural History Diorama of a Devonian Reef Source: http://clccharter.org/angelique1/Devonian/devonian.html
Materials Needed for Visit
Your vehicle needs a Michigan State Park sticker on your vehicle, GPS, water bottle, back pack, good sturdy hiking boots, newspaper to wrap fossils, and (optional) rock hammer. *Visitors are allowed
to collect a 5 gallon bucket of fossils a day. Please bring any trash out with you!
Directions:
1. Use your GPS to reach each stop.
2. At each stop, please reread the background material provided at the Earth cache page and then answer the questions pertaining to each spot that are posed.
3. To receive credit for this Earth Cache, please email your answers to the questions for each stop back to me.
Stop 1: Loading Docks/Stockpile Spoils: N 45. 1209 ◦ , W 83.2301
◦
You are now at the old Rockport old loading dock foundations. As you look east out into Lake Huron, you will observe remnants of the old Rockport loading facilities for the crushed limestone for ships.
Envision yourself back 80 years ago being at this place, this is what you would have saw shown below.
The rock crushing and conveyor belt distribution center for feeding the ore dock at Rockport.
Source: http://www.friendsofrockport.org/historyofrockport.html

Source: http://wsh060.westhills.wmich.edu/MGRRE/
Question 1: Now the
Devonian limestone occurs in circular deposits representing the weather exposed rims of the Michigan basins at this time as it was being filled up with sediments as do the other sedimentary rock features of the
Michigan’s Eastern U.P. and L.P. Look at the map below showing where quarries for limestone occur in this Devonian rock in
Michigan. What do you notice geographically about the location of most all the circles representing quarries for limestone? Why?
Now look southeast, you will notice a boat launch and parking lot, this is where back in the 1950’s after the quarry had been shut down, the caissons were built for the two towering piers on the Mackinaw
Bridge. The caissons allowed the towers, whose function was to anchor and support the cable holding up the suspension part of the bridge, to be secure to the bottom. Caissons are watertight structures or chambers, within which work is carried on in building foundations or structures
below water level, providing the foundation construction container for the tower’s piers to the lake bottom.
Source: http://web2.geo.msu.edu/geogm ich/limestone-mining.html
Question 2: Why do you think Rockport was an ideal location to complete this work? Cite specific reasons.
Caissons are being built at Rockport in the first two pictures and what they were used to build in the third picture.
Source: Mackinaw Bridge Authority - http://updigit.uproc.lib.mi.us/cdm/search/collection/macbrdg
Source : Mackinac Bridge Authority - http://updigit.uproc.lib.mi.us/cdm/search/collection/macbrdg
Source : Mackinac Bridge Authority - http://updigit.uproc.lib.mi.us/cdm/search/collection/macbrdg

Now look north, you will see the stock piles of crushed limestone that were never shipped.
Question 3: Why mine limestone? Look at the diagram below and send me a list of 5-10 specific items or uses that exist at you home that is related to this natural resource we mine called limestone.
Source: http://mstimms-gcse.blogspot.com/2012/10/summary-uses-of-limestone.html
Stop 2: Fossil Collecting in the Bell Shale and Rockport Limestone: N 45.1202
◦ , W83.2309
◦
You are now going to hike to an area in the old quarry to visit the ancient Devonian ecosystem that used to thrive in shallow, clear, warm sea when this area of Michigan was located by the equator over 350 million years ago. Make sure you have water, your backpack, correct shoes, newspaper, and rock
hammer. Please bring everything back that you brought out including your garbage. The types of fossils you find not only tell you the type of animal you have, it can also give you an idea where in this reef
complex this fossil might have originated. The reefs of this time were composed mainly of solitary and colonial corals and stromatoporoid (ancient sponges). There were other types of organisms inhabiting these reefs like moss-like colonial branching or mat like animals named bryozoans, crinoids and blastoids ( stalked starfish like sea lilies), clams (pelcypods), brachiopods (stalked bivalves), ammonites
(squids-cephalopods), trilobites, gastropods (snails), and boney placoderm fish. *See diagram below.
Devonian Reef Cross-section
Bioherm
Source: Devonian Fossil PowerPoint,
Carl Wozniak, MESTA 2014 Alpena
Field Conference
Turbulent water environment Calm water environment

As you look east from the road you are walking on now, you will observe a mound of clay running parallel for 100 feet along the road known as the Bell Shale. It is the rock layer below the Rockport limestone. These shale areas represent calmer water environments and the fossils have been easily weathered out and can be easily picked up or dug out. Shale layers can also be found in the limestone layers are known as shale facies and can be found in the calm water environments between bioherms and the wave torn, turbulent areas on the reef. North, sout, and west of your current position there is an abundance of the fossiliferous Rockport limestone where occasionally you can find weathered out fossil specimens (whole or fragmented), large heads of corals and stromatoporoids, but many fossils are still embedded within the limestone itself. Watch your foot holds, look where you step, depending on how far you go, there can be some rough terrain. Enjoy!!!
Quest ion 4: What type of fossils did you find?
Email me a list of some key fossils that you found and what part of the reef complex you think they might have come from. If you want,
attach some pics! Below are some of my finds.
Alpena Area Stratigraphy or Rock Layer Sequence
Source: Source: Devonian Fossil PowerPoint, Carl Wozniak, MESTA 2014
Alpena Field Conference
Rockport
Quarry
Formations
Source: Personal picture from 2014 MESTA Conference Rockport Quarry Field Trip

Source: Personal picture from 2014 MESTA Conference Rockport Quarry Field Trip
Earth Science Literacy Principles Big Ideas:
Big Idea 2. Earth is 4.6 billion years old.
2.1 Earth’s rocks and other materials provide a record of its history. Earth scientists use the structure, sequence, and properties of rocks, sediments, and fossils to reconstruct events in Earth’s history.
Big Idea 6. Life evolves on a dynamic Earth and continuously modifies Earth.
6.1 Fossils are the preserved evidence of ancient life. Fossils document the presence of life early in Earth’s history and the subsequent evolution of life over billions of years.
6.8 Life changes the physical and chemical properties of Earth’s geosphere, hydrosphere, and atmosphere. Living organisms produced most of the oxygen in the atmosphere through photosynthesis and provided the substance of fossil fuels and many sedimentary rocks. The fossil record provides a means for understanding the history of these changes.
Big Idea 7. Humans depend on Earth for resources.
7.1 Earth is our home; its resources mold civilizations, drive human exploration, and inspire human endeavors that include art, literature, and science. We depend upon Earth for sustenance, comfort, places to live and play, and spiritual inspiration.
7.2 Geology affects the distribution and development of human populations. Human populations have historically concentrated at sites that are geologically advantageous to commerce, food production, and other aspects of civilization.
Common Earth Science Misconceptions for:
Big Idea 2. Earth is 4.6 billion years old.
• There is one geologic column for the whole earth.
• All rocks are more or less the same (a rock is a rock!)• Geologic time can be described using hundreds of years ago.
• It is easy to understand the amount of geologic time that has passed for changes on the Earth’s surface to occur.

Big Idea 6. Life evolves on a dynamic Earth and continuously modifies Earth.
• Life on Earth cannot modify or cause change in the Earth’s systems.
• It is easy to find fossils.
• Fossils tell us everything about the past
• Fossils are man made
Big Idea 7. Humans depend on Earth for resources.
• "Man-made" materials do not come from mineral resources.
• Few products we use every-day have anything to do with taking rocks and minerals from the ground.
• Rocks have very little practical use.
• Geologic and social history cannot be found in rocks.
References:
1. Black, T., personal communications. *Based on a field trip Ty lead for the MESTA conference at the
Rockport quarry on August 15, 2014. **Ty is a retired DEQ geologist who is a Michigan karst expert and led the ground work to get the Rockport quarry designated as a state recreational area, with the key idea to promote Michigan’s geological history by allowing park patrons to collect Devonian fossils on their visits.
1. Dorr, J, A. and Eschman, D, F. “Geology of Michigan”, The University of Michigan Press, Ann Arbor,
1987.
2. Ehlers, G. M.; Kesling, R. V. “Devonian Strata of Alpena and Presque Isle Counties, Michigan”
Museum of Paleontology Publication, 1970. * Can be downloaded as a PDF at http://deepblue.lib.umich.edu/handle/2027.42/48601 *Contains plates of photographed fossil specimens, along with the paleoecology and geology of the Alpena area.
3. “Fossils of the Michigan Basin” * Digital pictures of over 300 Devonian fossils from the Alpena area http://michiganbasinfossils.org/ Accessed 8/20/2014.
4. Mackinaw Bridge Authority - http://updigit.uproc.lib.mi.us/cdm/search/collection/macbrdg
5. Wozniak, Carl. “Devonian Fossils of the Alpena Area” PowerPoint Presentation, MESTA Alpena Field
Conference, August 13-16, 2014