Much of what we know about large river ecosystems comes from work on regulated rivers. The scarcity of quantitative information about pre-development conditions on these rivers restricts understanding of the full range of ecological responses to regulation and constrains predictions of future regulated-river behavior in the context of climate change, continued water development, management and restoration efforts. River regulation in the Colorado River basin has changed the magnitude and timing of water and sediment delivery to downstream reaches. Channel narrowing is a widely documented morphological adjustment of stream channels to natural or anthropogenic changes in stream flow and sediment flux, including establishment of vegetation on formerly active channel features. The Yampa River is perceived as one of the least regulated rivers in the Colorado River basin. We examine the degree to which the Yampa has been altered by water development. Further, we mapped geomorphic features and compared riparian vegetation across three distinct channel planforms. Of seven major Colorado River tributaries, the Yampa is the fifth largest in terms of virgin mean annual discharge. However, it is has the second smallest degree of flow regulation, expressed as the percent of virgin mean annual discharge capable of being stored, and retains a high degree of flow variability. Analyses indicate significant differences in plant species cover and composition among channel types (p=0.001). Significant differences in vegetation also were related at a finer scale to specific geomorphic surfaces (e.g., active channel, active floodplain), reflecting distinct geomorphic processes and physical environmental conditions. Finally, there were no significant changes in vegetation cover or frequency on specific active bar surfaces over four years implicating the importance of flow variability. This information provides a baseline for gauging future channel change and can be used to tailor change-detection monitoring to hypothesized geomorphic and vegetation changes in specific hydrogeomorphic settings.