Hydraulic gold-mining tailings produced in the late nineteenth century in the Sierra Nevada foothills of California caused severe channel aggradation in the lower Feather and Yuba Rivers. Topographic and planimetric data from historical accounts, maps, topographic surveys, vertical sections, aerial photographs, and LiDAR (light detection and ranging) data reveal contrasting styles of channel change and floodplain evolution between these two rivers. For example, levee cross-channel spacings up to 4 km along the lower Yuba River contrast with spacings <2 km on the larger Feather River. More than a quarter billion cubic meters of hydraulic-mining sediment were stored along the lower Yuba River, and the wide levee spacing was intentionally maintained during design of the flood-control system to minimize delivery of sediment to navigable waters downstream. Consequently, the lower Yuba floodplain has a multithread high-water channel system with braiding indices >12 in some reaches. Some of the larger of these channels remain clearly visible on aerial photographs and LiDAR imagery in spite of intensive agricultural leveling. Narrow levee spacings on the Feather River were designed to encourage transport of mining sediment downstream and keep the channel clear for navigation. Levee spacings on the lower Feather River reached a minimum near the turn of the twentieth century, when floodplain widths were reduced at several constricted reaches to <250 m. Historical data indicate that the general channel location of the lower Yuba River had stabilized by the end of the nineteenth century, whereas substantial channel avulsions began later and continued into the twentieth century on the lower Feather River. The striking contrasts in channel change between the Yuba and Feather Rivers are due, at least in part, to different river-management strategies, although the Yuba River received much more sediment. Early river engineering of these channels represented the first efforts at integrated river-basin management west of the Mississippi, so the observed long-term effects are instructive. Modern river management should consider how the disturbance factors in these channels and the imprint of early river management affect the modern morphologic stability and sediment-production potential of the channel and floodplain.