The Folsom Dam Joint Federal Project is being undertaken to increase the spillway capacity of Folsom Reservoir in order to meet the demands imposed by an updated assessment of the probable maximum flood. The auxiliary spillway consists of an approach channel from the reservoir, a control structure, and a spillway chute and stilling basin that discharge spillway flows into the American River downstream of the existing spillway. The stability of the rock slopes upstream of the control structure and approach walls were evaluated using kinematic analyses to screen for critical geometry followed by limit equilibrium analyses of the kinematically-feasible cases to design slope reinforcement where necessary. Variability in the joint orientations was accounted for using a probabilistic analysis based on the measured scatter in orientation for each joint set. A fully three-dimensional (3D) analysis of the approach channel sidewalls, taking into account both existing and planned excavation geometry, existing and planned rock slope reinforcement, and the planned reinforced concrete approach walls, was also performed.