Ground balance question for CZ's

I recently went to Arizona on a "get away from the snow vacation".I took my CZ 70 and the 5" coil.I was attempting to ground balance on a sandy beach along the Colorado river.I found a spot in all metal with no targets and bobbed the coil as always.It would ground balance at between 9 and 10.I checked this in 5 more places.I checked in all metal to make sure there were no targets before I ground balance.It would balance at between 9 and 10 in all the spots.I had to turn the sensitivity down to 4 as even at 4 it would false a lot.Underneath the sand was a sticky red clay(iron?).I got about 4 to 5 inches in depth maximum.Found a bunch of clad and 1 silver ear ring.The coins were really corroded.I later saw some bands of white salt or alkali mineral streaking on the top of the ground back away from the beach area.Any thought or ideas on the ground balance numbers.Signed "Back in the Snowdrifts"Bill

Bad laterite with salts and Fe3O4. Not good! Difficult to hunt.

Thanks Tom.I figured it was bad ground.Bill