History of the OKI-RCC Landscape

The OKI Regional Conservation Council consists of nine county conservation districts in what is known as the Tri-State.  Others refer to this nine-county region as Greater Cincinnati.  It encompasses Butler, Clermont, Hamilton and Warren counties in Southwest Ohio; Boone, Campbell and Kenton counties in Northern Kentucky; and Dearborn and Ohio counties in Southeast Indiana.
The Tri-State has been blessed by Ice Age creation of the Ohio River.  It served as a major commercial artery in the early and mid-1800’s, transporting grain and livestock to the Mississippi River and down to the port of New Orleans.  In the 1830s, with the construction of the Miami & Erie Canal, Cincinnati became the primary center of processing and trade on the Ohio River.  Cincinnati’s population went from less than 10,000 residents in 1820 to over 115,000 residents by 1850.  This spurred the creation of other industries.  The local meatpacking industry gave rise to Procter & Gamble, which used the byproduct lard to make soap.  Machine tool operations located in the Mill Creek Valley and along the Miami & Erie Canal, where they used the flowing water to power their plant equipment.  The region’s clay soils fostered many brick-making establishments and the world-renowned Rookwood Pottery.  The region’s solid industrial base, burgeoning work force, and growing population has justified the construction of railroads, Ohio River locks and dams, state and interstate highways, and the August 1944 opening of what is now officially titled the Cincinnati/Northern Kentucky International Airport.  Better known as CVG, the airport is a prime example of regional collaboration because it is located in Boone County, owned by Kenton County, and attuned to the needs of more than a dozen counties in the Tri-State region.

The foundation for this unique landscape formed 450 million years ago when the area lay in a coastal zone and alternating layers of shale and limestone were deposited up to 400 feet thick.  This was followed by a period when the area was covered by a broad, shallow sea filled with coral and myriad sea creatures.  This period saw the development of a thick, fossil-filled limestone cap over the area.  The final geologic act to shape our Tri-State region into what it is today saw successive advances and retreats of massive glaciers over much of North America beginning 1.8 million years ago.  These glaciers pushed as far south as the current location of Ronald Reagan (Cross County) Highway in Hamilton County, scraping the landscape and blocking ancient rivers that flowed northward in the region.  The damming of these rivers created massive reservoirs in the valleys of Eastern Kentucky and West Virginia.  These reservoirs eventually broke through and carved the Ohio River Valley.  When the glaciers receded, they left massive pockets of sub-surface gravel forming the Great Miami Buried Valley Aquifer System, an important source of drinking water for many communities north of the Ohio River.  The melting glaciers also carved the innumerable stream valleys and deposited fine clay soils for which the region is known.  The glaciers also provided rich soils present between the Ohio River Valley and the glacial Great Lakes.

The Tri-State region belongs to two physiographic provinces: the Till Plains section of the Central Lowland Province and the Interior Low Plateaus Province.  The boundary between the two is commonly drawn along the Ohio River, even though some scattered, old glacial deposits occur along inter-stream divides south of the river.  Both provinces are underlain by flat-lying sedimentary rocks and a long-inactive basement.  Absence of much glacial cover south of the Ohio River largely accounts for the prevalence of steeper slopes in Kentucky in the Outer “Blue Grass section of the Interior Low Plateaus Province.  Dearborn and Ohio counties are also mostly in slopes.  The Southeast Indiana counties belong to the Dearborn Uplands, a small segment of the Central Lowland Province.

North of the Ohio River, in areas underlain by deposits of Wisconsinan and Illinoian glacial drift, valleys are present near the major streams.  Areas of older or no drift sheets, the landscape is more deeply dissected by streams. The steepest slopes are located below Cincinnati along the Ohio River, where the river impinges and undercuts a valley wall.  This cut bank consists of soft Kope shales capped by more resistant limestones, which form bluffs with even greater slopes.  Some of the valley sides of the Licking River have comparable slopes for the same reasons.

In contrast to the deeply dissected topography described above are the poorly drained flat uplands of Clermont and southeastern Warren counties.  These areas are developed on the Illinoian till plain, which has had about 300,000 years for weathering to smooth and flatten its original glacial topography.  The much younger Wisconsinan drift sheet, no more than 19,000 years old, commonly has a gently rolling topography and much better drainage.  Both the younger and older drift sheets have modified the Tri-State’s terrain by filling its deep valleys with till and outwash.

Upland elevations across the region are uniform, ranging from about 825 to 900 feet above sea level.  The highest elevations occur in northern and southeastern Warren County on scattered outliers of Silurian carbonates, which stand 35 to 55 feet above Ordovician sedimentary rocks.  The local relief – the difference between the highest and lowest elevations in a county – is also restricted, averaging about 530 feet.  In the Tri-State area and across the Cincinnati Arch, these upland elevations define a regional erosion surface described as the Lexington Peneplain.

Geology and hydrology have molded the landscape and driven the growth of our geographically gifted region.  The OKI Regional Conservation Council is dedicated to preserving the benefits of our dynamic geological history.

The region’s topography is illustrated above. The dark brown represents severe slopes (greater than 20%), the light brown represents moderate slopes (11%-20%), and the white represents slight slopes (0%-10%).


A website and a printed publication served as the key sources of information for the geological history above.  They are:

Ohio History Connection, Ohio History Central, Bedrock Geology of Ohio http://www.ohiohistorycentral.org/w/Bedrock_Geology_of_Ohio

Exploring the Geology of the Cincinnati/Northern Kentucky Region, Today’s Landscape and Its Heritage (pg. 12) by Paul Edwin Potter for the Kentucky Geological Survey, Series XI, 1996, Special Publication 22