The California State Parks are celebrating their 150th anniversary in 2014. They are kicking off the celebratory year with 40 different hikes on New Years Day (January 1, 2014). I went on the website to see if any of them were at a state park in the Delta. The only Delta county with a hike is Sacramento, but both hikes were in Folsom. My curiosity was peaked: how many state parks are there in the Delta? Two. Brannan Island State Recreation Area offers day use and camping. The other park is Delta Shores and appears to be closed due to the state budget cuts.
There are 26 reviews of Brannan Island SRA on Yelp. Brannan Island is in Rio Vista in Solano County (about 30 minutes from Fairfield). Although there will not be an organized hike, the weather forecast suggests New Years Day is a good day to enjoy the park.