I just got back.
A spot too far downstream from a gold source can have virtually all of the nice indicator rocks and amazing looking gravel bars and still not have an appreciable amount of gold because gold is 5 times heavier than anything else in the river except platinum. So there will be a bottom edge of nice prospects that fail to pan out
If you have found wonderful indicators but little or no gold it would be well to work further and further upstream.
Unless you reach a point where the indicators too dwindle away to nothing, eventually you should start finding gold.
Once you find gold if it is too scarce keep going upstream until the gold suddenly, or fairly suddenly stops. Then go to the last edge where you found any and up the bank. As long as you find any gold keep moving uphill. When the gold stops, this time move in the downstream direction a few yards at a time until it reappears.
Keep working uphill as you try to stay as far upstream as possible and still be able to pan out even a little gold.
If you do this with diligence you are likely to eventually find the spot where the gold is eroding from the mountains into the river, like an exposed vein or an ancient stream-bed that erosion has uncovered.