The exposed and abandoned Teays Valley has been recognized and studied in south-central Ohio for a century and a half. By 1900, the upper reaches had been traced by bedrock strath up present deeper drainages through West Virginia into Virginia. By 1945, the 1.5-mi-wide main valley had been traced downstream by water/oil wells, under several glacial drifts, northward and westward from Chillicothe, Ohio, to Indiana. The average gradient in this reach is northwest 0.9 ft/mi. Horberg and others carried this valley westward to the Mahomet buried drainage of Illinois. Discontinuities such as in Madison County, Ohio, have been explored by geophysical profiles and test wells and show a marked narrowing into a canyon cut through resistant dolomites. As late as the 1970s, the largest tributary, which drains most of eastern Kentucky northward and on either side of Cincinnati, has been added. More and more basal floodplain sands/gravels and northward-inclined crossbeds are found in all these meandering valleys beyond the glacial limit. Near the limit these deposits are covered with lacustrine clay rhythmites, which grade to silty and then into sandy outwash containing glacially derived northern clasts. Clearly, glaciation dammed the valley system westward out of Ohio. This blockage was early Pleistocene, certainly pre-Illinoian, because clays are magnetically reversed. Other blockages took place southwestward from Cincinnati at a later date. The exposed Minford Clays in southcentral Ohio and western West Virginia must have filled to near the present 900-ft contour, because the former, dendritic Teays drainage is criss-crossed by an aimless, superimposed drainage that postdates the Deep Stage.

At some time during the Pleistocene Epoch, a part of the modern Ohio River drainage system in Ohio and West Virginia developed in response to impoundment of the ancestral Teays River drainage system. Rhythmites formed in the lacustrine slackwaters and remain today, extending as much as 150 to 200 km upstream from the Pleistocene ice front, in Teays Valley, West Virginia. A total of 303 oriented paleomagnetic specimens represent a composite stratigraphic section from the Minford Silt Member of the Teays Formation in Teays Valley. Of these, 224 specimens carry a stable reversed magnetization due to detrital magnetite and hematite. Two distinctive lithologic intervals with definitive magnetic intensities were found in the stratigraphic section; thick, light-colored rhythmites carry six times more remanent magnetization intensity than thin, dark-colored rhythmites, reflecting variations in the ratio of magnetite to hematite. From the Pleistocene paleomagnetic chronology, the glacial diversion of the Teays River in Ohio and West Virginia took place during the Matuyama reversed polarity chron, in the time interval between 0.79 and 1.60 Ma, the change attributed to an Early Pleistocene age, most probably the F or G glaciation. We propose that the Minford Silt was deposited between 0.79 and 0.88 Ma.

Three transects were conducted across the main channel of the abandoned Teays River valley in Pike, Jackson, and Scioto Counties, Ohio, to evaluate the lithology and general stratigraphy of valley-fill deposits. Field observations obtained from both deep borings and surface excavations indicate that much of the Pleistocene lacustrine fill has been removed and that the modern landscape reflects primarily a sequence of erosional and secondary fill surfaces. Thus, the current valley fill includes lacustrine clays and channel sands, as well as younger sediments of varied origin. A general sequence of three sedimentary stratigraphic units was commonly encountered in the transects. A silty surface unit overlay an intermediate deposit, which in turn, rested on channel sands or on highly laminated lacustrine materials that were equated with the Minford Clay Member of the Teays Formation. The silty surface unit occurred at almost all sites to a depth of 50 to 60 cm. The mineralogy was mixed, and clay-free particle-size profiles indicated the material was loessial in origin. The intermediate deposit was also encountered in most borings and could be classified as colluvial, alluvial or lacustrine depending on the location. The lithology of this deposit was highly variable and frequently reflected the properties of local bedrock units. Minford Clay was distinguished from younger lacustrine sediments of the intermediate unit on the basis of higher clay content, more micaceous mineralogy, and an elemental Zr content that was two to four times less. Discriminant statistical analyses of data from a total of 180 samples indicated that the Minford Clay could also be easily distinguished from all other Quaternary sediments in the Teays Valley on the basis of selected chemical attributes. By using the same parameters, however, lacustrine deposits in overlying stratigraphic units could not be clearly separated from associated colluvium, alluvium, and loess.

The Old Kentucky River system was a major contributor to the Teays River, draining southwestern Ohio and much of eastern Kentucky. The trunk river flowed northward from southeastern Kentucky throughout Frankfort and Carrollton, and then past Cincinnati and Dayton, joining the Teays River near Springfield, Ohio. North of the glacial boundary, which lies along the modern Ohio River, the course of the Old Kentucky River has been modified, and is today largely buried by drift. Although dissection is extensive to the south, there are many remnants of this entrenched and broadly meandering Teays-age valley system and of its sub-upland predecessors. These valleys contain areas of upward-fining, deeply weathered gravel, composed mainly of rounded quartz, chert, and silicified limestone pebbles derived from the headwaters of the system. Modern rivers have been entrenched 30 to 100 m below the Old Kentucky River valley and its main tributaries, the Old Licking and South Fork. The Old Kentucky River system was severed from the Teays when glaciation dammed its downstream reaches, forcing a reversal in flow direction between its junction with the Teays in west-central Ohio and Carrollton, Kentucky, and causing westward overflow into the Old Ohio River system. Piracy by the Old Ohio may also have contributed to the integration of the Old Kentucky and Old Ohio River basins. Ponded sediment is present in some of the now-abandoned valley remnants east of Cincinnati. As a result of glacial damming, the headwaters of the Teays River in southeastern Ohio and West Virginia overflowed westward across the Manchester divide into the Old Kentucky River drainage basin. All of these events led to establishment of the modern Ohio River system.

Configuration of the buried part of the Teays Valley system across western Ohio, Indiana, and eastern Illinois suggests that the Teays is not a preglacial system, but rather, that it was formed marginal to a major glacier earlier than that which created the Ohio River, probably in similar fashion by consolidating and diverting fragments of older drainages. Pertinent criteria include (1) the relatively straight gorge that (2) crosses at least three regionally high areas with (3) few tributaries that join at grade. Also significant are (4) the depth of the gorge across a broad limestone plateau that has (5) relatively shallow karst development. These features imply a youthful valley system that was destroyed by burial before reaching a mature stage. Although thousands of drillholes and seismic datum points in Indiana alone detail the bedrock surface and the nature of the unconsolidated deposits that overlie it, many questions remain regarding the evolution of that surface. Fluvial and lacustrine deposits associated with the earliest presently known till in Indiana (>0.8 Ma) fill eastern parts of the Teays gorge. Are there tills of pre-Teays age, and is any part of a pre-Teays valley system identifiable? What stratigraphic criteria distinguish those parts of the Teays that have been reoccupied and incorporated into younger, but now also buried, valley systems? The Blue River Strath of southern Indiana shares many characteristics with the type Teays and the ancestral Kentucky River valley and may be coeval with them; are there other such features? A regional approach to these and related questions should yield results.

The Lafayette Bedrock Valley System is a complex of bedrock valleys that converge on and diverge from Lafayette, Indiana. The primary trunk valley of the system, composed of the narrow Marion Valley Section on the east and the broad Mahomet Valley Section on the west, is the classic “Teays Valley” of the Midwest. If such a continuous Teays drainage truly existed, it represents only the early part of the history of the Lafayette Bedrock Valley System in Indiana. Origins of the valley parts and their form remain enigmatic. Although the Marion crosses major rock structure, the course and the contrasting forms of the parts reflect structural and lithologic control. Contrasting valley forms, valley deeps, and possible inset benches may reflect one event or multiple events in a single valley, or disparate events in other valleys; or the features may reflect external events, such as incision through forebulge or erosion beneath bursting ice dams. Although the origins of the valley system are conjectural, the fill sequences within give evidence of the nature and timing of the demise of the system. The Marion valley is filled with a plug of old lacustrine and glaciolacustrine sediments included in the Blackford Member of the Banner and Jessup Formations. These sediments were deposited in a lake dammed between ice at the valley bends at Logansport, Indiana, and St. Marys, Ohio. Deposited at the dams were subaqueous fan deposits of coarse-grained outwash and tills of both basal-meltout and sediment gravity-flow origin. The tills include the red claystone-bearing West Lebanon Till Member on the west, and the Wilshire Till Member on the east. An uppermost tongue of the West Lebanon till caps the Blackford lacustrine sediments, indicating southeastward progression of the West Lebanon ice into the lake and ultimately over the entire fill sequence. The relative age of plugging of this valley section is suggested by the West Lebanon, which overlies magnetically reversed (>0.7-m.y.-old; marine isotopic stage 22?) sediments in western Indiana. The plugging of the Marion valley by West Lebanon ice corresponds in time with the plugging of the valley in Ohio by Wilshire ice (and the deposition of the Minford Silts) and marks the end of classic Teays-stage regional drainage. The Mahomet valley subsequently was reexcavated as part of a Metea-Mahomet drainage system, heading in northeastern Indiana. This valley is filled with younger, interfingered outwash and till, which are included in the Mahomet Member and the Brookston Till Member of the Banner and Jessup Formations. These deposits represent aggrading braided stream and fan environments in front of southwestward-advancing Brookston ice. The relative age of plugging of this valley section is given by the Vandalia Till Member of the Glasford Formation, an Illinoian till that caps the valley fill, and by the West Lebanon till, which was apparently cut out prior to valley filling. The final plugging of the Mahomet marks the end of any deeply incised drainage in north-central Indiana. With the demise of the Mahomet drainage outlet, development of an upper Wabash drainage system began. The fill of bedrock valleys south of the Marion-Mahomet trunk valley contains evidence of multiple erosional surfaces. The gradients of these surfaces suggest a merging at Lafayette into early equivalents of the modern Wabash drainage, exiting into the Wabash bedrock valley via the Attica cutoff or across the rock sill above Independence.

Groundwater resources associated with sediments filling the Marion and Mahomet Valley Sections of the Lafayette Bedrock Valley System vary from miniscule to substantial, reflecting the wide range of glacigenic aquifer facies contained in the fill. These aquifer facies include braid-stream deposits that range from thin units within till sequences to immense, valley-filling masses. Also included is a variety of proximal to distal, subaerial to subaqueous, fan and fan-delta deposits; these range from thick masses of ice-proximal, cobbly rubble interspersed with thin diamicts and clays, to thin, discontinuous lentils of sand confined within lacustrine clays. Valley-fill aquifers are confined by capping till units, except where exhumed at the crossings of the Maumee-Wabash Trough (modern Wabash River Valley). A variety of aquifers typically are available within the valley-capping sediments; for this reason, much of the deep valley-fill has not been extensively explored or developed. Some valley-fill aquifers are so thin and/or deeply buried that their exploitation is unlikely, but others are so thick and areally extensive that exploitation easily can support sustainable yields of tens of millions of gallons per day.

The buried Mahomet Valley in east-central Illinois is a complex lowland carved into the surface of Pennsylvanian and older rocks. It consists of a deep channel throughout most of its length and contains numerous benches below erosional remnant hills, suggesting several cycles of early to middle Quaternary erosion. Recent local and regional studies utilizing existing borehole data, including down-hole geophysical logs and seismic profiles, have provided new insights into the valley’s configuration. The usual techniques for interpreting shallow seismic refraction and reflection data are complicated by a seismic velocity inversion in the Quaternary sediments filling the deeper parts of the valley. Based on the 500-ft (152 m) elevation contour to define the upper limit of the Mahomet Valley Lowland, the valley is about 8 mi (13 km) wide at the Illinois/Indiana border. Westward, the lowland widens to as much as 18 mi (29 km) in Ford County, where a major tributary enters from the north. Here, several ridges rise above a broad bench ranging from 400 to 450 ft (121 to 137 m) in elevation. Sparse well data and some seismic profiling suggest a deep channel at or slightly below an elevation of 350 ft (106 m) in northeastern Ford and northwestern Vermilion Counties. This deep channel extends southwestward where it passes under the villages of Mahomet (Champaign County) and Monticello (Piatt County) and then westward to just east of Clinton (De Witt County). Between Mahomet and Clinton, where there are also several isolated bedrock hills that rise to elevations as much as 500 ft (152 m), the intermediate bench lowers to 350 to 400 ft (106 to 121 m). The valley narrows to an average of 14 mi (22 km) wide between Monticello and its confluence with the Mackinaw Valley segment of the Ancient Mississippi Bedrock Valley in southwestern Tazewell County. Southeast of Clinton, a narrow bedrock “diversion” channel (Kenney Valley) provides a nearly straight connection between the Mahomet Valley and the Ancient Mississippi Valley below the confluence with the Mahomet. A complex Quaternary history has been established for the Mahomet Bedrock Valley, but as yet no evidence has been found for late Tertiary or preglacial alluvial deposits. Deposits filling the valley include the widespread Mahomet Sand Member, as much as 200 ft (60 m) thick, locally overlying or interbedded with tills of the Banner Formation (pre-Illinoian). Above this succession are Glasford Formation (Ulinoian) and Wedron Formation (Wisconsinan) tills and associated deposits. The varied nature of the bedrock valley topography, the scattered presence of till-like material on bedrock hills underlying the Mahomet Sand, and the presence of lower Banner Formation till interbedded with the Mahomet Sand suggest several episodes of valley erosion and glacial deposition during a long pre-Illinoian history. The deepest bedrock channel probably originated before deposition of the Mahomet Sand but postdates at least one early Quaternary glaciation. Near the Indiana border, the uppermost surface of the Mahomet Sand, at elevation 560 ft (170 m), appears locally eroded, forming broad terraces that continue down valley at progressively lower elevations. The surface of the Banner Formation forms a broad sag over much of the valley and rises slightly over the uplands. Deposits of the Glasford Formation form the upper fill in the valley and include a significant outwash related to the Vandalia Till Member. The Sangamon Soil, developed in the Glasford, together with the overlying Roxana Silt and Robein Silt, locally forms an important subsurface marker. The topographic expression of this pre-Woodfordian surface shows no evidence of the Mahomet Valley; it was completely buried by the end of the Illinoian. Aquifers associated with the Mahomet Bedrock Valley and the Ancient Mississippi Bedrock Valley to the west are the only highly productive, nonalluvial sand and gravel aquifers in the southern three-fourths of Illinois. The aquifers associated with the buried Mahomet Valley provide the only large source of irrigation, industrial, and municipal supplies of groundwater in east-central Illinois; 40 municipalities and water districts are currently obtaining groundwater from these aquifers. The largest groundwater withdrawals occur in the Champaign-Urbana area, averaging 17 × 10 6 gal (64 × 10 6 l/day. Total groundwater withdrawals from the valley are estimated to be at least 42 × 10 6 gal (16 × 10 7 l)/day. The coefficients of storage for the Mahomet Sand range from 2 × 10 −5 to 2 × 10 −3 , with hydraulic conductivities and transmissivities up to 4,237 gpd/ft 2 (2 × 10 −3 m/s), and 510,000 gpd/ft (5 × 10 −2 m 2 /s), respectively; for the Glasford sand the coefficients range from 1 × 10 −5 to 8 × 10 −2 , with hydraulic conductivities and transmissivities up to 4,660 gpd/ft 2 (2 × 10 −3 m/s), and 233,000 gpd/ft (2 × 10 −2 m 2 /s), respectively. Coefficients of vertical hydraulic conductivity of the confining beds range from 2.12 × 10 −3 to 0.4 gpd/ft 2 (1 × 10 −9 to 2 × 10 −7 m/s).