Mountainous regions are the primary source of water for much of the western United States. Many mountain streams are sustained by groundwater, but conceptual and hydrologic models often oversimplify groundwater processes. As a result, it is challenging to predict how streamflow responds to changes in groundwater recharge and storage caused by extreme wet and dry conditions. This project is evaluating how groundwater regulates stream responses to hydrologic extremes by integrating high-resolution stream and groundwater observations with hydrologic models. The knowledge generated from this work will improve understanding of how stored groundwater impacts mountain streamflow generation, thereby enhancing streamflow predictions. Broader impact activities include an early-career workshop on data-model integration in Earth surface processes, with the goal of fostering cross-disciplinary collaboration. Additionally, the project will integrate field infrastructure and models into undergraduate coursework at three institutions to expose more students to hydrologic science. This project aims to determine the role of groundwater in regulating streamflow response to hydrologic extremes across a groundwater storage gradient using a data-model integration approach. Field observations of stream discharge, source, and age in two mountain watersheds will be integrated with an iteratively calibrated process-based hydrologic model capable of simulating groundwater-surface water interactions