A hydrogeologic framework was developed for unconsolidated Quaternary deposits at the U.S. Army Atterbury Joint Maneuver Training Center. The framework describes the potential for the occurrence of ground water on the basis of physiography and the distribution of geologic materials within the study area. Four geologic units-the Jessup, Trafalgar, Atherton, and Martinsville Formations-were identified, and their distribution was mapped as four hydrogeologic regions. The Jessup and Trafalgar Formations are fine-grained, poorly sorted tills. At least two facies of the Atherton Formation, the lacustrine and outwash facies, are in the study area. The Martinsville Formation includes materials deposited or reworked since the glacial period. With the exception of the Atherton Formation outwash facies, the Quaternary deposits are primarily fine-grained, silt- and clay-rich sediments that function as confining layers or aquitards. The Atherton Formation out-wash facies includes sand and gravel deposits that constitute the primary aquifers in the study area. The four hydrogeologic regions mapped in this investigation are designated as the Bedrock, Jessup Till, Trafalgar Till, and Atherton Outwash Regions. Each region represents an area with a distinctive physiographic expression and vertical sequence of Quaternary deposits. The Bedrock Region in the western and southwestern part of the study area commonly is underlain by 0 to 15 feet of Martinsville Formation resting directly on bedrock. Potential ground-water yields are limited. The Jessup Till Region in the southeastern part of the study area includes the uplands on either side of the stream valleys. Sediments commonly range from 30 to 90 feet in thickness. This region includes clay-rich till of the Jessup Formation and sand and gravel deposits of the Atherton Formation outwash facies; the Atherton Formation outwash facies tends to be thin, and ground-water yields will be moderate. The Trafalgar Till Region in the north and northwest-central part of the study area commonly is underlain by 10 to 30 feet of Trafalgar till or Trafalgar till over 25 to 50 feet of Jessup till. Within, separating, and beneath these tills are deposits of the Atherton Formation outwash facies-the sand and gravel deposits with the best potential to support a water-supply well. Generally, the outwash facies in this region are thin sand and gravel lenses, except in a few locations that are in excess of 30 feet thick. The Atherton Outwash Region is the lowland area associated with the major valleys in all but the far southwestern part of the study area. This region has the greatest thickness of outwash facies sands and gravels (often in excess of 20 feet), which are the primary aquifers. In the Atterbury Joint Maneuver Training Center, the combined Atherton Outwash Region and the Trafalgar Till Region have the greatest potential as infiltration areas because of low topographic relief and(or) sandy soils. From water-level data collected in July and August 2003, horizontal ground-water flow was determined generally to be toward the Atherton Outwash Region and the valley of the Drift-wood River to the east. Vertical hydraulic gradients were documented at nested well pairs. At two sites, upwardly directed gradients are reflected by flowing wells. Ground-water discharge to surface water is likely in some eastern reaches of the valleys of Nineveh and Lick Creeks. In the valley of Nineveh Creek, potential for ground-water discharge is indicated by the presence of a flowing well, upwardly directed vertical hydraulic gradients, and ground-water heads that were higher than surface-water elevations. In the valley of Lick Creek, ground-water discharge also is indicated by the presence of flowing wells and ground-water heads that were higher than surface-water elevations.