The name Middendorf Formation has been widely used in the Coastal Plain of South Carolina, eastern Georgia, and southern North Carolina since 1904, despite conflicting interpretations of the age and stratigraphic relations of the unit at its type locality. Between 1995 and 1998, the U.S. Geological Survey, in cooperation with the South Carolina Department of Natural Resources, drilled three continuously cored holes to the south and to the east of the type section of the Middendorf Formation, which is located in Chesterfield County, South Carolina. In addition, two outcrops to the northeast of the type section were sampled for biostratigraphic control. The litho- and biostratigraphic relations of the units in these cores and outcrops provide significant insights into the age of the Middendorf Formation at its type locality, and how this age impacts regional correlations of the formation. A projection of formational contacts and thicknesses from downdip areas into the type locality of the Middendorf Formation indicates that the type section is most likely a facies of either the uppermost Bladen Formation (of the Black Creek Group), or the uppermost Bladen and the lowermost part of the Peedee Formations. This report documents the evidence that support this interpretation. The implication of this interpretation is that the name "Middendorf" has been applied to a variety of units throughout the southeastern United States, all of which display a similar lithology, but differ significantly in stratigraphic position and age. For these reasons, we recommend that the name Middendorf be restricted for use with strata that occur only in the vicinity of the type locality, and use of the name "Middendorf" for units elsewhere in the Coastal Plain be reconsidered.