Your favorite park may already have an operating agreement in the works. Get in touch with them and find out if there are any local non-profits that are supporting that park directly. In some cases the California State Parks Foundation will match donations, doubling your impact!
Donating may not always be the best way to help. Some parks may need volunteer time, some might ask for your presence at the state capitol, and some might just need a signature. It’s important to understand each park’s particular situation so you know how best to help.