Gold being carried by the flow of a river drops out just as soon as the flow can no longer keep the gold moving. The heavier pieces of gold and other heavy rocks tend to drop out first with the finer materials dropping out last as the flow or the pressure of the flow diminishes to the necessary amount. Now that's real nice however the reality here is that many things cause the water flow/pressure/velocity to change such as deep sections of water, obstructions (trees, Big boulders, crashed UFO's, etc.). Some of these obstructions to the flow change yearly along any given river location while outcroppings of hard bedrock take a long time to wear down so one might be able to count on what happens each year along any outcropping.
All of this movement depends on how many Cubic Feet per Second of water (CFS) has come down any given river way, the slope of the river bed along any given point of the river, how long the highest volume of water lasted and how quickly it drops. A lot of this is why gold is found in what seems like an odd or unusual location and, as well, why gold is not found along all parts of any given water way. "Gold is where you find it!" has been a phrase that sums it all up into one nice neat little package of words and why we prospectors must sample/test, sample/test, etc.
Persistence, learning and equipment all influence our finds. I started with a plastic cereal bowl and a T-spoon and now I'm up to a variety of gold pans and digging tools, a sluice box, a suction dredge and a prospector type metal detector and all of them have their uses. Prospecting is tedious hard work and sometimes it pays off. Kevin in CO has even gone through some of this though I suspect he's refined his tools to the minimum level and that is a real blessing as it limits what one must carry in to their own particular spot.
The best of success to your searching for the yellow metal!...........................63bkpkr