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[3] CRADDOCK T., HARDER L., VERIGIN S., KUTTEL J., BROWN D., MIHYAR M., BOYER D. Oroville Dam Spillway Incident – Fast Track Recovery Design to Address Critical Dam Safety. ICOLD World Congress Proceedings, 2018. [4] SNOW C.A., SHERER H. Terranes of the Western Sierra Nevada Foothills Metamorphic Belt, California: A Critical Review. International Geology Review, 2006, Vol. 48. [5] O’NEILL A.L., COKE K.J., MARLIAVE E.C. Geologic Report on Preliminary Exploration of the Oroville Dam Site. California Department of Water Resources, Project Geology Report No. 20-11-05, 1955. [6] HUBER O.L., GROSS D.J., MARLETT J.W. Final Geologic Report, Oroville Dam Spillway. California Department of Water Resources, Project Geology Report No. C-38 (20-11-26), 1970. [7] LAMKIN B.L., GLICK F.G. Oroville Dam Spillway, Results of Landslide Evaluation. California Department of Water Resources, Project Geology Report No. 20-11-35, 2004. [8] DUNBAR S., HOIRUP D., BARRY G.R. Oroville Dam, Emergency Spillway, and Flood Control Outlet, Drill hole and Shear Wave Velocity (Vs) Results. California Department of Water Resources, Project Geology Report No. 20-11-50, 2017. [9] DAM SAFETY REVIEW BOARD. Oroville Dam, FERC (Federal Energy Regulatory Commission) Project 2100-CA, State Dam No. 1-048, NID No. CA00035, CA00530, & CA83096, Ninth Five-Year Part 12D Safety Inspection Report, 2014 Director’s Safety Review Board, December 2014. [10] INDEPENDENT FORENSIC TEAM. Oroville Dam Spillway Incident Forensic Investigation Team (IFT), Preliminary Findings Concerning Candidate Physical Factors Potentially Contributing to Damage of the Service and Emergency Spillways at Oroville Dam, Forensic Team memorandum, May 5, 2017. SUMMARY Starting on February 7, 2017, a scour hole formed in the concrete-lined Gated Spillway chute at Oroville Dam. Continued intermittent releases between February and May 2017 led to further damage of the Gated Spillway chute and the creation of a large erosion scour channel to the left of the lower chute. During this time, the unlined Emergency Spillway was used for the first time to release reservoir flows. Significant erosion and scour of the weathered rock at the unlined 120