This data release consists of tables with the thickness and particle-size characteristics of overbank sediment deposited in May 1978 along the valley of Powder River in southeastern Montana. About 900 sediment samples were collected at regularly-spaced distances from 20 valley transects along a 90-kilometer reach of Powder River between Moorhead and Broadus, Montana. The decrease in sediment thickness and particle size with distance from the main channel showed weak trends, which were caused by the variability introduced by vegetation sediment traps and subsidiary channels.