The Geology of Lee’s Summit, Missouri

Lee’s Summit is a city in the state of Missouri, located in the west-central part of the state. With a population of over 97,000 as of 2020, it is one of the largest suburbs of Kansas City. The geology of Lee’s Summit provides insights into the ancient natural history of the region.

The bedrock foundations of Lee’s Summit consist primarily of limestone, shale, and sandstone formed during the Pennsylvanian subperiod of the Carboniferous period, approximately 300 million years ago. These sedimentary rocks were deposited as marine sediments in shallow inland seas that covered the central United States at that time. Since the Carboniferous period, the Lee’s Summit area has undergone millions of years of erosion, uplift, and exposure to create the landscape seen today.

Pennsylvanian Bedrock

Limestone

The bedrock beneath much of Lee’s Summit consists of cyclical sequences of limestone, shale, sandstone, and coal that characterize the Pennsylvanian subperiod. Limestone makes up a significant portion of this bedrock. Pennsylvanian limestones were formed from the accumulation of calcium carbonate from shelled marine creatures and chemical precipitation in warm, shallow inland seas.

The relatively pure limestones in the Lee’s Summit area include the Bethany Falls, Ladore, Swope, Dennis, and Cherryvale formations. These units range from gray to brown in color and contain marine fossils such as brachiopods, bryozoans, and crinoids. The limestones are interbedded with other rock types including shale, sandstone, and coal.

Shale

Shale is a fine-grained sedimentary rock formed from the compaction of clay, silt, and mud. During the Pennsylvanian, black organic-rich shales were deposited in low-oxygen environments within the inland seas. The Heebner, Cherryvale, and Weir-Pittsburg formations contain dark gray to black shales within their sequences.

Compared to other rock types like limestone and sandstone, the shales are more easily weathered and eroded. The presence of these weaker shales has influenced the topography of the Lee’s Summit area.

Sandstone

Sandstones within the Pennsylvanian bedrock represent nearshore deposits along the shallow inland seas. Quartz sand derived from the erosion of granite and gneiss in the Appalachian Mountains was transported by rivers and streams westward where they accumulated as beaches, bars, and dunes.

The sandstones are typically buff, brown, or gray in color and exhibit rounded quartz grains cemented together by calcite or silica. Notable sandstone units include the Pawnee Limestone, Labette Shale, and Bandera Shale formations. The geometry and thickness of sandstones were influenced by the shape of the shoreline and sediment supply.

Coal

Interbedded within the Pennsylvanian bedrock sequences are coal seams, indicating the presence of ancient peat swamps along the coastal plains bordering the inland seas. Plant debris accumulated in these swamp environments, eventually transforming into coal through heat and pressure.

Major coal deposits are found within the Weir-Pittsburg, Cherryvale, and Marmaton formations which contain extensive shale sequences that formed in low-lying swamps. These coal seams have been locally mined around Lee’s Summit since the late 19th century.

Glacial History

While Pennsylvanian-aged bedrock forms the foundation of Lee’s Summit geology, the overlying sediments record more recent geologic processes. Most significantly, Lee’s Summit was profoundly impacted by continental glaciation during the Pleistocene Ice Age, which spanned from about 2.5 million to 11,700 years ago.

Pre-Illinoian Glaciation

The earliest period of glaciation in Missouri is known as the Pre-Illinoian glaciation, which occurred between 2.5 million and 500,000 years ago. Pre-Illinoian glaciers originated from centers in present-day Canada and expanded southwards into the central United States. These massive ice sheets carved out and scoured the landscape, leaving thick deposits of gravel, sand, silt, and clay.

In the Lee’s Summit area, Pre-Illinoian glacial sediments consist of reddish-brown sandy clays. Although subsequent erosion has removed most Pre-Illinoian deposits, some remnants have been identified in the Missouri River bluffs north of Lee’s Summit. These ancient glacial sediments provide evidence that the region was overridden by continental ice sheets prior to the more recent Illinoian glaciation.

Illinoian Glaciation

From 300,000 to 130,000 years ago, Lee’s Summit and the surrounding areas experienced the Illinoian glaciation. Advancing from eastern Canada, the Illinoian glaciers reached their maximum southern extent in Missouri. This continental glaciation profoundly shaped the topography and drainage systems of the Midwest.

In the Lee’s Summit area, the Illinoian glaciers deposited thick layers of till – unsorted sediments directly laid down by ice. These tills consist of clay, sand, gravel and boulders in a heterogeneous mixture. When the Illinoian ice sheets melted back, they left behind rolling till plains dotted with depressions, ridges, and hills.

Exposures of Illinoian till can be seen along roadcuts, streambeds, and quarries around Lee’s Summit. The iron-rich clays weather into a distinctive yellow-orange color. Illinoian tills provide nutrients for productive farmland but their thickness and clay content also pose engineering challenges.

Loess

In addition to glacial tills, the Illinoian period was accompanied by extensive deposition of loess – wind-blown silt. As Illinoian glaciers melted, huge amounts of rock flour were released into the Missouri River drainage system. Prevailing westerly winds picked up these fine silts and deposited thick blankets of loess across the Midwest.

Loess deposits consist of porous, buff to grayish silts and clays that can reach up to 60 feet thick in the Lee’s Summit area. Loess accumulations partially bury and overlay the rolling Illinoian till plains. The loess helps create gently rolling, fertile prairies suitable for agriculture in this region.

Post-Glacial History

Following the retreat of the Illinoian ice sheets, Lee’s Summit has experienced about 100,000 years of post-glacial weathering, erosion, and drainage development. A few major aspects of the post-glacial geological history are highlighted below:

Drainage Systems

With the melting of the Illinoian glaciers, immense quantities of meltwater flowed down the Missouri River valley. Erosion from these glacial outwash streams helped carve out and establish the modern Missouri River drainage basin.

In the Lee’s Summit area, the embrace of the Little Blue River and its tributaries deeply dissect the till plains and loess hills. Stream downcutting has exposed bedrock bluffs, creating a stepped topography between uplands and river valleys. Ongoing erosion and deposition along these river systems continue to slowly alter the local terrain.

Karst Topography

The abundance of limestone bedrock around Lee’s Summit has led to the development of karst features. As acidic rainwater infiltrates cracks and pores in the limestone, it gradually dissolves and enlarges openings. This process creates sinkholes, losing streams, springs, and caves.

There are over 200 mapped sinkholes in the Lee’s Summit area, typically forming in clusters or alignments along joints or fractures. Sinkhole densities tend to be higher where the limestone is relatively pure and thick. Though individually small in size, the sinkholes demonstrate the easily eroded and karstified nature of the bedrock.

Soils

In the most recent millennia, soil formation processes have created complex soil profiles across the Lee’s Summit landscape. Soils derived from loess deposits tend to be highly productive for agriculture, though erosion can be problematic on steeper slopes. Reddish clay-rich soils have developed over Illinoian tills. Shallow lithic soils exist where erosion has exposed bedrock. Ongoing pedogenesis continues to modify local soils.

Key Formations

Here is an overview of some of the key geologic formations that shape the bedrock geology of Lee’s Summit:

Bethany Falls Limestone

• Light gray, dense limestone with interbedded shale
• Formed in shallow marine environments
• Abundant marine fossils including brachiopods, bryozoans, crinoids
• Forms bluffs and quarries north of Lee’s Summit

Ladore Shale

• Dark gray to black organic-rich shale
• Deposited in low-oxygen conditions
• Contains thin limestone and fossils in lower layers
• Prone to slumping and mass wasting of slopes

Swope Limestone

• Thick-bedded gray limestone layers
• Cherty nodules common near the top
• Ledges form bluffs along Little Blue River
• Karst features well-developed where limestone is exposed

Weir-Pittsburg Shale

• Dark gray to black shale and mudstone
• Contains abundant coal seams
• Formed in coastal swamp environments
• Weathered shale forms soils with shrink-swell clays

Cherryvale Shale

• Black shale with siderite ironstone concretions
• Grades into sandstone and sandy shale
• Multiple thin coals near middle and base
• Prone to mass wasting on steep slopes

Unique Local Formations

The geology of Lee’s Summit includes a few unique rock units found only in this region:

Truman Road Shale Member

This shale within the Cherryvale Formation contains well-preserved shark teeth and fish bones, indicating the unit was deposited in a shallow marine environment. The rare fossils provide insights into Pennsylvanian sea life.

Blue Springs Siltstone Member

This distinctive crumbly blue-gray rock within the Wyandotte Formation crops out along Interstate 470 in Lee’s Summit. Its high clay content causes frequent rockfalls. The siltstone represents a tidal flat deposit.

Todd Member

This sandy limestone found within the Swope Formation contains halite crystal casts, gypsum veins, and ripple marks, suggesting deposition in a very shallow coastal setting. Its limited distribution makes it a unique Lee’s Summit formation.

Economic Geology

The geology of Lee’s Summit has strongly influenced economic activities from mining to construction aggregate to waste disposal. Here are some of the key economic geology factors:

Coal Mining

Coal mining targeted the Bevier, Weir-Pittsburg, and Little Kate coal seams from the 1880s to the 1960s around Lee’s Summit. Room and pillar mining extracted coal for heating and power generation. Abandoned mines now pose safety hazards.

Limestone Quarries

Numerous quarries in and around Lee’s Summit excavate high-purity limestone and dolomite for construction aggregate. Major carbonate units quarried include Bethany Falls and Swope Limestones. Dimension stone for buildings also extracted.

Clay and Shale

Shale units like Ladore, Cherryvale, and Weir-Pittsburg are used for manufacturing bricks and cement. Surface clay pits also mine Illinoian till and loess deposits for bricks, ceramics, and as a liner for the Lee’s Summit Landfill.

Petroleum Potential

Although not yet productive, the Cherokee Basin has undergone oil and gas exploration drilling. Organic-rich shales could source hydrocarbons and deeper formations may provide reservoirs. Small seeps reported locally.

Geologic Hazards

The geology of Lee’s Summit also presents some hazards and limitations:

Karst Issues

Sinkhole collapse is a threat where development occurs on limestone bedrock. Groundwater in karst areas is vulnerable to contamination. Storm runoff can rapidly recharge aquifers through sinkholes.

Mine Subsidence

Old coal mines underlying parts of Lee’s Summit present a risk of ground settlement as pillars give way. Homes and roads may incur damage. Mine blast vibration has also cracked foundations.

Shrink-Swell Clays

Abundant shale- and loess-derived clays undergo substantial shrinking and swelling with changes in moisture content. This cyclic change stresses and cracks foundations, roads, and structures.

Slope Failure

Steep bluffs and stream banks with shale or loess are prone to landslides and slumping, especially where undercut or saturated. Mass wasting can deliver sediment into streams following heavy rainfall.

In summary, Lee’s Summit sits upon a foundation of Pennsylvanian limestone, shale, sandstone and coal that was heavily modified by continental glaciation. Ongoing geomorphic processes continue to shape the landscape and influence the economy and hazards of the region. The geology provides key insights into the natural history of Lee’s Summit.