Just a little story of an incident that happened about a year ago: I had taken mgb to a spot on the Agua Fria to show him around. I noticed 2 little nodules of bedrock sticking up out of the overburden and told him there should be a nugget there. So, he took his MineLab 3500 over and within a couple of minutes, found a nugget weighing a little less than 1 gram, about an inch deep in one of the nodules.
In the meantime, I was detecting under the roots of an old oak on the edge of the embankment. I had a faint signal, apparently in the bedrock. So, I spent about 30 minutes moving the rocks and head-sized boulders out of the way. But, after all of my work, even though I was a lot closer to the bedrock, the signal had disappeared. I decided that since I only had the large 12.5" coil for my MXT, I had been getting a faint signal from a "hot rock", and gave up.
A few days after I went home (back down South), mgb wrote and said he had gone back out to the Agua Fria and found another, but larger, nugget. (He posted a photo of it) I don't recall the weight offhand, but, I believe it was over 5 grams. (I just spent over an hour searching for his post, turns out the nugget was 3.61 grams).
Still, a fine addition to anyones collection.
Anyway, the next time I was up here, we went out to the Agua Fria and he showed me where he found the large nugget. Yep, you guessed right. He found it under the tree roots where I had removed all of the rocks. He said that it was just laying there on top of the bedrock.
What I believe happened was; as I remove the rocks so that I could detect the bedrock, I was (unknowingly) getting further away from the nugget, as it wasn't on the bedrock, it was above, in the tree roots. Sometime after we left, the nugget broke loose and fell down onto the bedrock, and laid there long enough for him to return and find it.
The moral of this little story is; If your signal disappears, don't give up until you check in all directions to see if you can pick it up again.