Placer gold tends to deposit in areas of low water pressure. By this, I mean that anywhere the water slows, gold will try to find a resting place, while lighter gravels continue to wash down a river. When searching for these low pressure areas it is important to visualize the river during the runoff season as this is the time when the gold moves the most. If you are not able to visit the river during high water season, look for the high water mark. Look for the highest points on the bank where drift wood has been deposited. This is probably close to the high water mark.
Gold often travels down the gut of the river, taking the shortest path possible. This can be visualized by looking from the inside edge of a bend in the river up or down to the edge of the next bend. Look for anything that might obstruct the flow of water along this path. There might be a large boulder or other object that can break the flow of water. The down stream side of the object can catch gold.
Look for sections of bedrock that cross the river. If there are cracks or crevices crossing the flow of water, they can act as natural riffles in a sluice box. Surprisingly large pieces of gold can work their way into what appear to be small cracks. When a river widens, the water pressure decreases. This can allow gold to deposit.
The inside bend of a river causes water to slow enough that gold can be deposited on the bend along with other gravels that form a bar. Depending on the bar, placer gold can be concentrated on the up-river and down-river sections of the bar.
It can also be deposited in pockets throughout the bar. Flood gold, the gold that is easily moved during floods, can be scattered in the top layers of gravel thoughout the river with pockets forming in spotty locations. These are not the only places that placer gold can deposit, but they are some good places to start.
Now I highly recommend that you try sampling rather than just picking a spot and going for it. The goal of sampling is to locate a more richer section of gravel before you start gold panning. It is well worth the time and effort to sample so that you can find the pockets or paystreaks of gold. A paystreak is often a somewhat narrow stretch of river that has a higher concentration of gold than the rest of the river bed.
When sampling, don’t wast time trying to extract every flake or speck of gold from your gold pan. Look for a promising spot and pan it down until you can get a good idea of the number of pieces of gold that came from the hole. Make a note of the spot and move onto another promising spot. Continue to make note of the concentration of gold in each spot. Then, after sampling several spots, go back and work the spot that was producing the most gold.
If while sampling you discover a really good deposit. Take some samples upstream, downstream, and on the sides to find the boundaries of the deposit. This will let you know the general area of the gold deposit and you might just discover an even richer part of the deposit. I know that I would rather work the richest part of the deposit, if I was limited on time.
Once you have located a good spot, now is the time to slow down and really work the area. Pan the material down until you only have about a half a cup of material in your gold pan. At this point, you can see some of the gold and know whether or not you are still in a productive spot. Rather than spend a lot of time separating the gold from the other gravel, place it in a small bucket or container to cleanup at home. This way you spend more time getting the gold.