It looks like your membership has expired, Anonymous
FYI, Penfolds Magill Estate is just in Mount Lofty Ranges and not Adelaide Plains. It's not far away from Adelaide Hills which is just over the actual mountain range. This image is part of a massive project I'm working on and shows the area around Adelaide including the location of Penfolds.
Note that these boundaries came directly from Wine Australia's incredibly detailed maps and I drew them into Google Earth Pro.
Thanks, Mark! I've edited above.