I'm thinking "rectangle" is this little corner of the city of Novato boundary covered in various sections of natural=wetland.  The "Hamilton Wetlands" name should probably be applied with a leisure/protected_area=nature_reserve tagging to an area south of here.

Boundaries of the project are shown in a picture on this website, unfortunately in perspective that would make it difficult to use as a source.  I'll take a look for county government info on the land ownership.

https://natureinnovato.com/2018/01/23/hamilton-wetlands/