Question:
I will be in the San Francisco area for the weekend of August 12th of this year. I understand that there is also the Outlands (?) music festival going on in the park at that time. Will the entire park still be open, or will there be areas that will be off limits to anyone who didn’t buy a ticket tho this event?

Answer:

Here is a map that illustrates the sections of the park affected by the festival: 
http://www.sfoutsidelands.com/festival/festival-map.php . The fenced-in portion highlights the parts of the park that someone with a ticket cannot access. 

Enjoy your visit!