SF Bay Area Skid Pad?
 

Anyone know of a 200' diameter or larger skid pad in the Bay Area?

Apparently not ;)

There's a large skidpad at thunderhill. I was told by an HPDE organizer that
if you're there for an HPDE and ask the track owners if you can use the skidpad,
they generally will permit it, as long as you have an observer there for safety
reasons. I have not put this to the test yet.

They'll only permit it if the HPDE organizer pays for it... a couple of guys tried this at an event I was at and it promptly got shut down and explained to everybody that if we want the skidpad, the cost goes up...