Which environmental event was the inspiration for Earth Day?

Answer: 1969 Santa Barbara Oil Spill

Wiki - The Santa Barbara oil spill occurred in January and February 1969 in the Santa Barbara Channel, near the city of Santa Barbara in Southern California. It was the largest oil spill in United States waters at the time, and now ranks third after the 2010 Deepwater Horizon and 1989 Exxon Valdez spills. It remains the largest oil spill to have occurred in the waters off California.
Live Science - Earth Day is an annual event created to celebrate the planet's environment and raise public awareness about pollution. The day, marked on April 22, is observed worldwide with rallies, conferences, outdoor activities and service projects.
Started as a grassroots movement, Earth Day created public support for the creation of the Environmental Protection Agency (EPA) and contributed to the passage of the Clean Air Act, the Water Quality Improvement Act, the Endangered Species Act and several other environmental laws. The idea for Earth Day was proposed by then-Sen. Gaylord Nelson of Wisconsin, who died in 2005.
The first Earth Day was in 1970. Nelson, after seeing the damage done by a 1969 massive oil spill in Santa Barbara, California, was inspired to organize a national "teach-in" that focused on educating the public about the environment.
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