The Recent delta of the Colorado River of Texas is an exceptional model for analyzing sediment and faunal facies relationships in environments associated with deltas. Because of the delta’s small size it is feasible to obtain closely spaced cores to provide the information essential for making a detailed facies study. Moreover, air photographs document (1) growth from a linear shoreline to the lobe-shaped deposit formed prior to artificial channeling of the river through a barrier island and (2) development of an 8- to 10-foot-thick platform of deltaic sediments, which divides Matagorda Bay, during the 6-year period following removal of an upstream log jam. This study of delta progradation was concentrated in the northeastern part of the Colorado delta, an area unaffected by manmade modifications. Continuous cores and borings define the deltaic facies complex and the underlying bay facies. The sequence of facies and environments from the surface downward is (1) delta-plain root-mottled clay and silt (1 to 5 feet thick) with "algal crusts" giving way locally to massive and burrowed clays of the channel-fill environment; (2) delta-front sand (2 to 8 feet thick), characterized by small-scale crossbedding, which grades laterally into finer grained sediment; (3) prodelta reddish-brown laminated silty clays (1 to 5 feet thick); and (4) bay laminated and burrow-mottled silty clays and clayey silts (10 to 14 feet thick), which lie unconformably on the Pleistocene. Color variations, together with X-ray radiographs recording laminations and burrows, are most useful in distinguishing between facies of bay and prodelta environments. The faunas characterizing the facies and environments are more variable than are the sediments; juvenile and small mollusks are more definitive than foraminifers. Two stages of delta progradation are indicated by air photographs; the earlier stage is represented by a parrowly lobate delta having closely spaced distributaries; the lafter stage, by a more digitate lobe that encircles the eastern half of the earlier lobe. A delta-front sheet sand was deposited during the earlier stage; bar-finger sands were formed when the digitate lobe was actively prograding. Sand distribution (that is, barfinger versus sheet) is probably related to variations in load and discharge caused by dredging of a channel when the latter delta lobe was forming. Subsidence of 1 to 2 feet is estimated to have resulted from compaction since initial delta formation, although locally as much as 4 feet of subsidence is documented. This volume was based on a symposium, Deltaic Sedimentation, which was held at the AAPG/SEPM Annual Meeting in New Orleans, Louisiana on April 1965. Many geologists have become involved in studies of deltaic sediments and sedimentation processes. Some of the papers in this volume are based on detailed local studies of modern deltaic sedimentary sequences, on processes of deposition, and on physical and biological characteristics of the deltaic environments.