A little late in the day but went for my afternoon walk and right around the corner was this nice PARK set up on Mission just west of 1st street. It looked pretty neat I wish I had arrived earlier. It's very odd to see so much green in an area I pass everyday, pleasant really.
To find out more National Park(ing) Day:
http://www.tpl.org/tier2_kad.cfm?folder_id=3428