Trail Ridge is a one mile-wide and 100-mile-long topographic ridge that separates the Okefenokee Basin and Swamp from the coastal plain of Georgia. It represents the crest of a former beach complex and was formed as inland sand dunes. The ridge is composed of fine-grained to medium-grained quartzose sand. The hydrogeology of the southern portion of Trail Ridge has been extensively characterized at a proposed mine site in southeastern Georgia. In the study area, the ridge is underlain by a shallow aquifer, locally known as the Surficial Aquifer, and forms a hydrologic divide between the Okefenokee swamplands to the west and the Saint Mary’s River to the east. Trail Ridge is a classic example of a topographically-driven hydrologic system. The water table is shallow and mimics the ground surface. Much of the precipitation that falls on Trail Ridge is returned to the atmosphere by evaporation and transpiration. Precipitation that is not evaporated or transpired to the atmosphere infiltrates to recharge the Surficial Aquifer. Groundwater recharge on Trail Ridge causes the water table to mound close to the land surface. In the absence of recharge, water would flow from the Okefenokee Swamp in the west [where water levels are at an elevation of about 120 feet above mean sea level (amsl)] to the east (where water levels are at an elevation of 80 feet amsl) and the water table would linearly decline to the east. Groundwater mainly flows from the centerline of Trail Ridge to the west and to the east and small amounts of groundwater discharges to local streams, particularly on the eastern side of the study area. Along the western margin of the study area, groundwater flow provides water to the Okefenokee Swamp and related wetlands. On the eastern side, groundwater provides base flow to streams.