Im glad Im not the only one finding this. All my best pans have been pulled from coarse deposits in logical drop zones (behind boulders, trailing inside bends), well above the current water levels. So far so good.
But it doesnt seem to matter where I sample, I get a few specks per pan from the surface. Then when I work an area, it either fades out as I get deeper, or holds bigger bits from the top 20cm then it fades out. If I keep digging down I hit a heavy grey/blue clay layer thats tough to break up and wash, but has a lot of fine flakes in it. The return to effort ratio drops way off.
My thought is that these spots are near the high water mark of steady winter flow, which shifts the coarse sand and gravel but doesnt carry much gold. The coarser gold has been flushed down by flash flooding. So Im slowly working my way upstream, hoping to hit spots where more chunky bits get stuck. If that doesnt pay, Ill start again where the chunky gold sits on the top, and take the surface layer off the whole dang lot. Thatll keep me busy until Christmas... 2020.