The way I see it is the surface would be laying on the top of the ground, or within an inch. Most finds are recovered from this point to 10" then the deep recoveries from this point to a couple of feet down. Past two feet-well either it's a big target, ideal conditions, and lots of energy digging the sucker out. 3-6 ft never been there, so I don't know what's called.
Hey ppperj alas feel when I hit a targe deeper than 6-7 in I should avbrought a shovel. Ihav mer parks near me you need a permt and it says sfce onlyI saw a definition that suface was to 6f deep nhat I would e consider digging that deep with out back hoe. lol