Holocene sediments filling the Lavaca River Valley comprise a transgressive fluvial-deltaic-estuarine sequence which was deposited during the past 10,000 years. Coarse fluvial sands which occupy the valley axis grade upward into deltaic sands and muddy sands. These are overlain by four lithologically distinct mud facies which reflect estuarine conditions. Several different sources of argillaceous sediment were important during deposition of this valley-filling sequence. Muds delivered into Lavaca Bay by fluvial discharge are volumetrically most important, comprising 75% of the total fine fraction. Wave erosion of Pleistocene sedimentary strata exposed along the bay margin is a less important but significant source of argillaceous sediment, making up 25% of the estuarine m ds. Sedimentation rates determined for the past 10,000 years are comparable to those reported for the past 100 years, but suggest increased rates of mud deposition in modern times.