Previous scientific research has documented channel narrowing on the Green River near Green River, Utah, but the exact timing, rates, and causal mechanisms of that narrowing have been the source of disagreement in the scientific literature. This thesis demonstrates that the Green River has narrowed in two separate periods during the last 100 years. The narrowing is driven primarily by changes in the hydrologic regime and not by the invasion of saltcedar. The channel narrowed between 1930 and 1938, when a shift from wetter than normal conditions to a period of draught led to a reduction in river discharge. Channel width then remained relatively stable until construction of Flaming Gorge Dam in 1962, despite the presence of saltcedar. Narrowing has occurred since dam construction. Detailed analysis of the formation of an inset floodplain deposit indicates that it formed by a process of vertical accretion, during incremental events. Inset bank deposits within the study area are composed primarily of particles smaller than 0.125 mm. Measurement of suspended sand distribution within the water column shows that particles of this size are carried in suspension by the 2-yr flood. Continued vertical accretion over time elevated the floodplain surface until inundation rarely occurs.