This study investigates how local governments can be effective and strategic in reducing greenhouse gas emissions. It examines Community Choice Aggregation in California, a policy through which counties and cities are affecting significant changes to the state's electricity system. The study finds that by 2025, counties and cities that adopt the policy are forecasted to exceed the state's ambitious renewable energy goals by 4748 to 7625 GWh, reducing emissions equivalent to 1.14 to 2.04 million metric tons of carbon dioxide, in addition to other energy and community effects. The policy diffuses along political and social grounds, particularly in communities with higher levels of support for the environment, Democratic and Green party voters, and more education. These findings underscore the opportunity presented by targeted policymaking approaches, showing the capacity of local governments to affect statewide changes. Local government policymakers should seek to move beyond "low-hanging fruit" policies and enact difficult, effective policies. Strategy in policy adoption and diffusion is discussed related to the potential to enhance local government participation with high-impact policies.