Numerous mountain watersheds in the Colorado Mineral Belt (CMB) are impacted by acid rock drainage (ARD) and acid mine drainage (AMD), which mobilize metals and rare earth elements (REEs) into surface waters. In the upper Roaring Fork watershed near Independence Pass, natural ARD from a highly mineralized tributary is the primary source of acidity and element loading into Lincoln Creek, with additional contributions from historical mining at the Ruby Mine. Despite known concerns about metal transport, the fate of REEs remains poorly understood in this system and other similar watersheds. This study focuses on the behavior of major ions, trace metals, and REEs in surface waters along a flow path receiving ARD and AMD inputs. The objectives were to (1) evaluate the transport, mixing, and attenuation of major solutes and REEs across stream reaches, and (2) characterize REE geochemical signatures, including their redox behavior and utility as tracers in ARD/AMD impacted systems. Filtered water samples from six main sites were analyzed by Inductively-Coupled Plasma Mass Spectrometry (ICP-MS) and Ion Chromatography (IC) methods, and results were explored through mass balance transport calculations, bivariate plots, shale-normalized REE patterns, and the cerium anomaly. Water chemistry in the Lincoln Creek basin reveals distinct geochemical fingerprints for the Ruby Mine (enriched in Ca, Mg, Mn, and Cd) and the Mineralized Tributary (enriched in SO4, Fe, Al, and Cu), with several metals showing increasing trends in recent years. REE fractionation patterns and Ce anomalies further distinguish source contributions and processes, with the Mineralized Tributary displaying MREE enrichment from natural pyrite weathering and the Ruby Mine exhibiting HREE enrichment tied to mine-derived flows. Most solutes showed a mix of conservative and reactive transport depending on site and season, while certain late-season metal concentrations at the Grizzly Reservoir inlet exceeded aquatic life standards. These results indicate that source composition mainly controls major solute and REE patterns in surface waters, with reactive transport processes selectively influencing the behavior of certain elements. This thesis advances knowledge of metal and REE dynamics in high-elevation, ARD-affected watersheds and supports continued monitoring and management in the Lincoln Creek basin.