I donated many plants to a local garden here in Santa Barbara, some really nice cocktail trees as well as tons of little seedlings. It was an absolute pleasure and I am so happy to visit and see my plants living the life. There are other projects like this, you just need to find them and get to work.
https://sbbucketbrigade.org/event/humanitarian-garden-project/Contrary to what many Americans believe, the local government is actually there to serve you and you only need to engage in earnest with the right person to reach a goal. My experience in CA has been that SB county is actually very excited to work with people who have passion, vigour, and the desire to make the area better. I am able to close down crazy mountain roads with my county annually at a reasonable cost for the express purpose of just skateboarding down them for example, and all I needed to do was engage the local permit dept.
I cannot recommend enough that people actually participate in local government and develop relationships. After all, we're paying for all those people and services with our tax money. If you've never tried, you shouldn't complain!