Rates of fluvial sedimentation exhibit spatial and temporal variability that is important with respect to the study of prehistoric archaeological sites. Sedimentation rates within fluvial basins vary in response to internal dynamics, geomorphic controls, and external factors including climate and tectonics. Fluvial rates of sedimentation may be estimated using sedimentary, pedogenic, biogenic, and radiometric evidence. Holocene rates of sedimentation vary by three orders of magnitude, as shown by radiometric data from numerous localities in North America. Sedimentation rates define rates of matrix accumulation in archaeological sites. These act as controls on site construction and site modification. Artifact densities, spatial patterning, and preservation are all conditioned by rates of matrix accumulation. These dimensions of prehistoric sites are critical to the evaluation of variability within and between archaeological sites and to the study of past settlement/subsistence systems.