Geology of Dearborn, Michigan

Location and Formation

Dearborn is located in southeastern Michigan, about 10 miles west of downtown Detroit. The city’s geology and landforms have been shaped over long periods of time by the movement of glaciers and the erosion of rivers and streams.

Glacial History

Dearborn’s landscape was formed during the last ice age, when glaciers repeatedly advanced and retreated across the Great Lakes region over a period of about 2 million years. The most recent glaciation, known as the Wisconsin Glaciation, carved out the basic features of Dearborn’s topography around 18,000 years ago.

As the Wisconsin glacier moved across the landscape, it picked up rock, soil, and sediment which scoured the bedrock. This abrasive process smoothed and striated the surface of the bedrock. When the glacier eventually melted around 14,000 years ago, all the rock and sediment trapped in the ice was deposited across the landscape as glacial till. This very unsorted mixture of clay, sand, gravel and boulders forms an important component of Dearborn’s soil composition today.

Modern Topography

Dearborn today has a relatively flat topography, with an average elevation around 600-700 feet above sea level. However, a few key geological features stand out:

• Rouge River – The river and its tributaries cut through glacial deposits and expose sections of bedrock. This creates occasional steep slopes and cliffs along the river banks.
• Grabens – Long depressions in the landscape caused by ancient fault lines running beneath the surface. Grabens can be seen in parts of Dearborn as linear valleys between ridges.
• Kettle lakes and depressions – Shallow lake basins formed by buried glacial ice blocks melting. These are seen along the Rouge River.
• Old glacial moraines – Slight ridgelines composed of glacial till and sediments deposited at the glacier margin.

Bedrock Geology

The sedimentary bedrock underlying Dearborn dates back 400-450 million years to the Paleozoic Era. Southwest Michigan was covered by warm, shallow seas at that time.

Local Bedrock Formations

The main bedrock formations below Dearborn are:

Bass Island Formation

• Light brown dolomite and shale
• Very fine grained
• Lays deepest below ground surface

Sylvania Sandstone

• Tan/buff colored sandstone
• Visible along Rouge River valleys
• More resistant to erosion than other local rocks

Detroit River Group

This group consists of layers of shale, limestone, and dolomites in shades of gray, brown and black. Detroit River rocks can be seen exposed along the Rouge River banks. Specific formations found in this sequence include:

• Lucas Dolomite – Gray/tan dolomite
• Amherstburg Formation – Gray limestone and shale
• Lucas Formation – Gray calcareous shale

Local Fossil Species

Fossils commonly found within these Devonian-aged bedrock layers include:

• Brachiopods
• Corals
• Crinoids
• Trilobites
• Cephalopods like squid and ammonites

Evidence of these marine organisms indicates Dearborn’s bedrock formed in ancient shallow seaway environments.

Surficial Geology and Soils

While bedrock shapes the foundation below Dearborn, the city’s surface geology and soils influence everything from agriculture to civil engineering to stormwater management.

Glacial Sediments

Much of Dearborn’s surface is covered by varying thicknesses of unsorted glacial till and outwash sediments. This can include:

• Till – Very poorly sorted mix of clay, sand, gravels and boulders
• Outwash – Better sorted sand and gravel
• Lacustrine clay and silts – Fine lakebed deposits

In some areas, these sediments are 100 feet thick or more. Well drilling logs help map sequences over 300 feet thick in places.

Alluvium

Along stream valley bottoms like the Rouge River, older glacial sediments are covered by more recent alluvium:

• Stream eroded sand, silts and clays
• Organic mucks and peats

These valley fill deposits provide fertile farmland but can be prone to erosion.

Drift Thickness Map

This map shows the variable depth to bedrock across Dearborn based on well log data:

Thicker sections in red, thinner areas in blue. Scale is feet below ground surface.

As the map shows, a graben area follows the Rouge River valley, while moraines and sediment zones cause the bedrock surface to vary.

Soil Types

The USDA’s Web Soil Survey lists up to 21 different soil series mapped within Dearborn. These soil types have developed from the glacial sediments through long term chemical weathering and organic matter decomposition.

Major Dearborn soil types include:

H5. Common Dearborn Soil Series

Miami Series

• Loamy soils formed in glacial till
• Deep, moderately well drained
• Found across central and south Dearborn

Conover Series

• Sandy soils formed from old outwash
• Very deep, somewhat excessively drained
• Found along Rouge River corridor

Granby Series

• Fine sandy loam formed in till or lacustrine deposits
• Very deep, somewhat poorly drained
• Often excavated for sand and gravel pits

Natural Resources

Dearborn’s geology has impacted historical natural resource exploitation and modern environmental management.

Sand and Gravel

Deposits of sand and gravel have been excavated across Dearborn for over 100 years to support concrete manufacturing and construction industries in Detroit. These resources originate from glacial outwash sediments.

Early sand and gravel operations removed materials with little regulation. Today, companies must conduct environmental reviews, protect groundwater, and reclaim sites.

Major mining sites once located in Dearborn include Cherry Hill Pit, Dix-Vernor Pit, Warren Pit, and Outer Drive Pit.

Groundwater

Dearborn utilizes groundwater pumped from deep glacial and bedrock aquifers. Common well depths range from about 100 to over 300 feet to reach adequate supplies.

High capacity wells can yield hundreds of gallons per minute for municipal and industrial use. Shallower wells under 50 feet serve many households.

Protecting groundwater quality is an ongoing concern, due to industrial contamination risks.

Rouge River Watershed

As part of managing regional water resources, Dearborn participates in Rouge River watershed conservation efforts:

• Reducing pollution from stormwater runoff and sewers
• Monitoring water quality and ecosystems
• Promoting riparian buffers and floodplains

These initiatives help mitigate some impacts of development on the watershed since European settlement.

Unique Local Places to See Geology

Many geological aspects of Dearborn can be viewed across the city, but several unique locations to spot interesting features are:

Rouge River Valley

The river corridor cuts through glacial sediments down to bedrock layers, exposing rock formations not visible at the surface elsewhere. Trails provide public river access.

Hines Park

Moraines, kettle lakes, and other glacial landforms are visible from trails winding through wooded sections of the park.

UM-Dearborn Environmental Interpretive Center

This center features award-winning educational displays on the region’s ecological and geological history.

Automotive Heritage Museum Sand Mine Exhibit

This exhibit documents the industrial history of local sand and gravel quarries that supported Detroit’s auto industry growth.

Conclusions

In summary, Dearborn’s landscape has been shaped over long periods by a variety of geological processes, including glaciation, erosion, soil formation and sediment deposition. Evidence of this remains visible across the area’s flat terrain, small ridges, river valleys, lakes and soils. While urbanization has altered the area, a unique Ice Age geography still underlies the city and will continue influencing Dearborn’s environment and development.