The Aucilla River of northwest Florida drains parts of the central panhandle of northwest Florida and a small area in southwestern Georgia. It traverses nearly 111 km through a 220,510 hectare basin. The slow-moving river carries little sediment and terminates in Apalachee Bay, a low-energy embayment in the northeastern most Gulf of Mexico. This coastal region, known as the Florida Big Bend, is characterized by mudflats, sea grass beds, and an absence of sandy beaches and barrier islands. Clastic sediments of the coast and shelf rest on a shallow-dipping carbonate platform. The upper surface of the platform is locally karstic. As a result, like other rivers in this region of northwest Florida, the Aucilla watershed is marked by sinkholes and disappearing streams. The fact that the river travels underground through part of its lower watershed serves to trap or sieve some of its clastic load. In the estuary, the undulating karst topography causes the estuarine and marsh sediments to vary in thickness from 0 to nearly 4.2 meters. In places, in both the estuary and lower river valley --as well as offshore-the Tertiary carbonate units are exposed at the surface. The concave-seaward shape of the coastline and its orientation with respect to prevailing winds result in low average wave energy. Sedimentation is therefore controlled by riverine and tidal forces. Twenty-seven push cores were collected in the study area and analyzed for texture. Four additional cores were collected to determine sedimentation rates using the Pb-2l0 dating method comparison data from two other Big Bend estuaries, the St. Marks and Steinhatchee, were also collected. Granulometric results from the Aucilla cores showed the sediment texture of the surficial sediments to be quite similar to that found in the other two estuaries and from other studies in the region. However, more interesting than the areally uniform surface textural data for the entire Big Bend were the downcore textural changes observed in the Aucilla cores ( as well as in the St. Marks and Steinhatchee cores). The mean grain size and standard deviation data remained unchanged with depth. From these data, the present day low-energy conditions in the region appear to have changed little over much of the Holocene. Sedimentation rates derived from the Pb-210 dating method were comparable to rates determined in other studies of similar environments, tending to be near the low end of the range values. The low rates are probably due to the low energy and sediment-starved conditions in the Big Bend.