Contra Costa County currently only has a mask mandate for indoor activities. The wedding will be outside so this should not be an issue, however, you may need to wear a mask when entering the building to use the restroom.
At this time, no proof of vaccination is required for the venue. Note though that many restaurants and places of business in the area are requiring proof of vaccination to enter. So if you are coming from out of town, you will want to be sure to have your vaccine card or photo of this for local dining and entertainment.
It may get a little chilly at night, so please bring a jacket to wear in the evening. Or you can warm up on the dance floor 😄