Here are some central questions and answers about the damage to the Oroville Dam and the fight to prevent a catastrophe: What is the Oroville Dam? Work on the Oroville Dam — the tallest dam in the country at 770 feet — started in 1957 and included the relocation of California State Route 70 and Union Pacific Railroad tracks. It was completed in 1968, creating what is now the second-biggest reservoir in the state, sitting on the Feather River about 75 miles north of Sacramento in Butte County.