River sediment is one of the most pervasive pollutants in the world. Excess amounts of fine sediment can reduce water quality, damage stream ecosystems, and harm aquatic life. Both natural and human-caused processes can add sediment to a river, such as tectonic uplift, landslides, and timber harvesting. Therefore, it is important to understand how fine sediment enters and moves through a rive system to inform policymakers and land-managers on effective ecosystem management. In this study, we determined how the relationship between river flow and suspended sediment changed among watersheds along the North Coast of California. We found a rise in suspended sediment concentration at median flows following extreme timber harvesting. Additionally, our results indicate that river flow and suspended sediment relationships are influenced by timber harvest activity, tectonic uplift, rainfall patterns, and near-channel environments. These results support previous findings that extreme land disturbance in a watershed, be it natural or human-caused, can change river flow and suspended sediment relationships. Our results suggest that policymakers and land-managers should take into account tectonic uplift when making regulation and should prioritize protecting near-channel environments.

High-resolution seismic images of lithospheric structures allow us to infer the tectonics that modified the lithosphere. We apply such methods to understand Cenozoic modification of the lithosphere by tectonic and magmatic processes in the tectonically active western United States. Using USArray Transportable and Flexible Array data, we present high-resolution images for three regions in this thesis. (1) In the Mendocino triple junction, we use a joint inversion of Rayleigh-wave dispersion data and receiver functions to obtain a new crust and upper Vs model to ~150km depth. The model shows four distinct, young lithosphere-asthenosphere boundary systems. A low-Vs anomaly beneath the Great Valley-Sierra Nevada reconciles existing slab window models with the mantle-wedge geochemical signatures in Coast Range volcanics, and explains the ~3 Myr delay of the onset of volcanism after slab removal. Uppermost mantle low velocities provide evidence for forearc mantle serpentinization extending along the Cascadia margin. (2) In the Colorado Plateau, a Rayleigh wave tomography model sheds light on the volcanism along the margins and plateau uplift. Strong upper mantle heterogeneity across the plateau edge results from the combined effect of a ~200-400 K temperature difference and ~1% partial melt. A ring of low velocities under the plateau periphery suggests that the rehydrated Proterozoic lithosphere is progressively removed by convective processes. Particularly, a high-Vs anomaly imaged beneath the western plateau adds evidence for a downwelling/delamination hypothesis [Levander et al., 2011]. Thermo-chemical edge-driven convection causing localized lithospheric downwelling provides uplift along the margins and magmatic encroachment into the plateau center. (3) In the final study, we developed a 3-D teleseismic scattering wave imaging technique based on the Kirchhoff approximation and 3-D inverse Generalized Radon Transform. Synthetic tests demonstrate higher resolution imaging for continuous, irregular interfaces or localized scatterers, in comparison to conventional methods. Applied to the High Lava Plains dataset, the transmission coefficient structure shows a deepening Moho near 117.6°W and three negative events that correlate well with the Rayleigh wave low-Vs zones. Images made with the Mendocino data clearly show rapidly decreasing lithosphere-asthenosphere boundary depths from the subduction to transform regime.