Placer gold is gold that has moved from its original source. It starts with erosion. Wind and rain, water seeping into cracks in the rock, expanding as it freezes, all working to break down mountains and free up minerals in the rock.
In the spring, when the snow melts and mixes with rain showers, all that runoff acts like a series of bulldozers pushing everything out towards the ocean. Sit by a stream in flood stage and you can hear the rocks and boulders clattering down stream.
The water turns to chocolate milk from all the silt suspended in the water column.
Well, the gold is moving too. From fine particles of flood or float gold, swirling along with the suspended sand and silt, to heavier nuggets bouncing or grinding along with the stream gravels.
If the water loses its energy, if the bulldozers slow or pause, the gold settles out and digs in its heels. Gold deposits on the inside bends of streams, because the water on the inside moves slower than the outside. It settles in pools below falls, in slack water areas where narrow channels spread out and slow down, behind rocks where the water eddies. It settles into cracks in the bedrock.
Gold settles wherever the stream stops shunting it along. If you want to find it, you have to visualize what the stream was like in the Spring. Look around, look at the high-water mark and imagine all that water. What was slowing it down?
If you can figure that part out, you can probably find gold.