The purpose of this study was to define the lithofacies and areal extent of the Fort Atkinson Formation (Maquoketa Group, Upper Ordovician) in the subsurface in Indiana. Two distinct lithologic facies (Members) of the Fort Atkinson Formation can be distinguished in the subsurface. The upper Shoaling Member consists of coarse grained crinoid-bryzoan grainstone deposited in a high energy depositional environment. Beneath the Shoaling Member is the Transition Member of the Fort Atkinson. This Member consists of alternating beds of shale and limestone which were deposited in depositional environments that varied from high to low energy. The Fort Atkinson is an important stratigraphic marker used to define four depositional provinces within the Maquoketa Group in Indiana. The four depositional provinces include the Maquoketa Shelf, the Overlap Ramp. the Cincinnati Shelf, and Michigan Shelf. / Department of Geology