Ancient River Beds
An ancient river bed is a river in which water once ran but not longer does. Some type of geological process such as an earthquake, landslide, mountain building etc. may have stopped the water running in its old path and diverted it elsewhere. An ancient river bed may also exist just several meters from a rivers current location – rivers constantly meander and change their paths over time.
The image below shows the changing path of the Mississippi river, some of the old paths would be several thousand years old and could be classed as ancient river beds –
If this river was a gold bearing river it would have simply dried up and left the contents that it carried (including gold) sitting on the grounds surface – this is called an ancient riverbed. As a result, ancient riverbeds usually lie one to three feet underground (depending on their age) as geological processes would have covered up the dried up gravels yet they will still retain their rich gold bearing gravels.
How to find an ancient riverbed
Finding an ancient riverbed is not as straightforward as it is to simply turn up at a current river or creek and begin panning for gold, however, it is a lot more lucrative if you know what to look for. An ancient riverbed leaves some signs of its previous existence –
- layers in a current rivers bank
- rounded stones
- alluvial gravels
- water loving plants growing in unusual places
Layers in a current rivers bank – If you are prospecting on a current river, you may see some rounded stones in the river bank several feet above the current rivers height. If these stones appear in the river bank and then disappear it could signify that the current river has cut a path through the ancient rivers path. Although they could also be stones from the current rivers travel down through the layers of earth, you will need to do some research digging.
Rounded Stones – If you see stones that are simply lying around on the side of a footpath or in a forest you will notice that generally speaking they have sharp, pointed edges. Only stones that have been eroded by the action of water are rounded, such as stones that can be found on a beach or in a river. So, if you re digging several feet into the ground while prospecting and you suddenly come across rounded stones, you can be pretty sure that you have found either an ancient riverbed or a different pathway that a river once took. Either way, gravels like these are unlikely to have been prospected before and are definitely worth a closer inspection.
Alluvial Gravels – alluvial gravels are those which look like they may once have belonged on the sand bank of a river. They would be sands and small stones that have been deposited as a river turned a bend. These would be found a couple of feet underground and could be a long way away from a current rivers path. These ancient riverbed alluvial gravels could be within several feet of an ancient pay-streak.
Water loving plants in unusual places – certain plants cannot grow without a substantial water supply, a prime example of this is the cottonwood plant. Gold prospectors often look for the cottonwood plant to signify where an ancient riverbed once flowed or even where there may be a v-joint in bedrock. A v joint is where two types of bedrock meet each other at right angles, they then trap the water that the cottonwood plant needs to grow. Gold will also be trapped in such a joint, usually large nuggets and flakes.Similarly, if you see a line of cottonwood plants traveling or several meters/tens of meters you may have found an ancient riverbed.
How to prospect an ancient river bed
If you feel that you may have found an ancient river bed the best thing to do is to take several test pans from several feet deep, pan them out and compare the resulting gold. For example if pan A has some gold, pan B has less gold and pan C has no gold, it would be fair to assume that the ancient riverbed is not flowing in the direction of pan A to C, therefore you should take another few pans from nearby locations but in a different direction. Always draw a map of such test pans, this can be easily done nowadays with I phones and GPS, that way you will eventually find the exact direction of travel of the ancient river bed and eventually you may find a completely un-prospected pay-streak :).