Bay Area Delta?

I live in a San Francisco but had an appointment in Pittsburgh last week and I never go out that way. Had to get gas and pulled over at Martinez. I thought it was quite beautiful in that area and noticed on my way up there were the State Park signs, like on for Ryer Isalnd.

Is there a town or gem up in those parts worth visiting? I never hung out on the Delta (heard it could be gritty), but would love to explore more. I went to Benecia a few years ago and thought it was very quaint...hope to discover more cool spots to make a day trip out of and looking for suggestions. Bonus points if they are kid friendly.