Hi Loamer
My understanding to surfacing is the gold in the area was super rich and sat close to the surface on an ancient clay layer or bedrock. The old timers basically took the lot !!! Leaving the hard layer underneath. Surfacing is the name given to this form of mining. It is difficult to find gold in areas marked surfacing for a number of reason.
For the old timers when they found these deposits it was EASY gold !!
Happy days.
Also every newbie to detecting sees this on a map and works the area with their magic stick. (please note for the record) I am guilty of this.
The photo you posted of the site at Moliagal was surfaced hard! The welcome stranger nugget was unearthed by a horse buggy wheel.
However some good nuggets were found extremely close to that monument ( not on the surfaced area ) as recently as a few months ago.
I couldn't help but notice the comment in regards to detecting puddlers. Be very careful with these sites they are our history and heritage, eventually they will return to the earth by erosion. I personally don't prospect the puddlers, we are lucky to still have them to appreciate now. The fine for desecrating a site of historic significance starts around the $2000 mark. And If you re wondering if anyone has been fined this amount for hitting a puddler, the answer is yes.
Sorry to sound like an environmentalist on a mission.
I am very proud of our heritage and how our ancestors calved the australian economy from the earth.
Cheers Ryan