Faults: Dikes or Outcrops; Potholes
Even though faults are normally hidden, they are in most cases exposed on both sides of the stream and the characteristics it has under the water can often times be foreseen somewhat accurately.
The kind of fault a prospector should be looking for in this case is not huge in size but the ones that most geologists consider to small to even map. Erosion under the water is usually a lot less than that on the close by exposed shoreline. The trapping ability a fault has to capture gold is normally as good if the lower portion is up stream or down stream no matter what it looks like on the top. Therefore a fault is a good idea to look into.
Dikes or Outcrops
In most cases dikes and outcrops in a stream rarely have the sharp outlines that can be seen in pictures. Due to the fact that stream gravels have been eroding for a good number of years they often times look like big boulders resting on bedrock. Just as in the case of boulders, these should be checked out as a riffle to see whether the probable point of deposition is up or down stream.
Potholes
Potholes are usually formed at an area where the bedrock is softer or in an area where it is more exposed to erosion and abrasion. As opposed to what a lot of people believe they can be formed in places where the water eddys. In some cases a little portion of the bedrock is much softer in comparison to the material around it that it is simply hollowed out. One good case in point is where there used to be a mineral deposit that was softer than the transporting rock. On other occasions a big rock can fall causing it to rip out a piece of the bedrock.
In some instances there are potholes that are very big and these can reach up to twenty-five feet in diameter in larger rivers. Eddies are not always the cause of potholes, eddies in some cases are caused by potholes though.
As in the case of all geological structures, potholes go through several stages of development and they react in different ways to each stage of the action of the river. When they are comparatively new and small, debris and materials have a tendency of sliding over them abrading the hole and making it larger and depositing some or no heavier material. As these get bigger, material that is heavier is the trapped inside them and kept by the sands that pack the pothole full and not much more abrasion occurs to increase the size of the pothole. At this point of development the pothole is something that becomes interesting for a prospector or gold dredger to look into and a little one can have a good amount of gold in it.
Sadly to say, potholes are in most cases buried under the bed load and there is not a lot of indication that can be provided on the surface that shows where they exist or are located. Potholes are normally found by people that are dredging to bedrock and some depressions are so little that a dredger might even clean them out without realizing the pothole was responsible for most of the gold that was obtained that specific day.
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