Unfortunately different cities have different ideas about restrooms in their parks. In the east bay Walnut Creek parks restrooms are open and getting cleaned regularly. Danville and Concord to the South and North have closed theirs. I thought I would do a little research for cyclists using the Iron Horse Trail but that’s as far as I got. Every city hides that information in it’s own unique way don’t you know. Two weeks ago I chatted with a cyclist who had driven over from Pinole to ride in Walnut Creek since the Bay Trail restrooms were all closed. Those are run by EBRPD who has closed all their restrooms as noted above. For some reason they have also turned off all their drinking water.
I will leave finding further information as an exercise for the reader. Happy riding.