Go on Youtube and find Monterey Magnet Man, he magnet fishes and detects you can see some areas he goes to. Your AT Pro probably won't do good in wet sand but in the dry it will do fine. When I come down there I hit all the playgrounds in the parks and have found gold jewelry and silver jewelry...
It is pretty bare bones missing the foot treadle and the wheel. I wouldn't pay more than $10.00 myself. But my Sister owns 7 (Singers, New Home and Whites) all need refurbished but in semi decent condition. They were all free.
I agree with DizzyDigger, areas around Taft might be good but I think out around Highway 58 and Weed patch highway is one of the earliest settlement areas.
Detecting is a treasure hunt so obviously if you are out detecting you are seeking lost treasure. A story is how all treasure is found, buried caches, stolen loot from train robberies or bank robberies.
No all clasps are not magnetic and the corrosion also gave mine away. But I'll weigh my 2 chains up and you can send me the $ minus 35% so you can make a profit on my Ghetto gold.
Put a magnet to the clasp. I have found 2 gold chains marked 14k Italy both were fake or what I refer to as Ghetto gold. They sell a lot of fake gold at the Joyeria stores, Mexican jewelry stores.