True bedrock is the underlying host of any gold-bearing area, wet or dry, in which all the surface materials rest atop. The bedrock could consist of granite, serpentine, gabbro, gneiss, etc., which pose a complete barrier to the downward movement of placer gold, in other words, the final resting place of gold in any stream or wash.
Sometimes true bedrock will be found relatively close to the surface with only a few inches of overburden (sand, dirt, or gravel) covering it, or it could be buried under overburden as deep as 10, 20, or even hundreds of feet. Regardless of the depth of overburden, true bedrock will be the underlying foundation of placer gold deposits.
In many cases where placers are located, true bedrock is not readily visible. That’s because most of the existing bedrock has been covered by various layers of overburden that can include “false” bedrock layers composed of clays or “caliche” as well as layers of rock, sand, dirt, and gravels.
Unlike true bedrock, false bedrock is composed of various types of clay or successive clay layers, forming an extremely hard impermeable layer that prevents the transition of gold to lower points in any given stream or wash. As long as the gold DOES NOT meet an impermeable layer like true or false bedrock, it will continue downward either continually as it does in a running stream, or intermittently as it does in dry or desert placers.
Unlike true bedrocks however, false bedrocks can sometimes be found in multiple layers at various depths. This does not necessarily mean that each layer of clay (or caliche) will have gold resting on it. Sometimes it will, and sometimes it won’t, depending upon when and where the false bedrock layers were laid in time and space. Digging into the false bedrock itself will usually not reveal any gold, however, depending upon when the additional layers of false bedrock were laid, they may contain even better and more extensive gold values than the first layer.
So, unlike true bedrock which exists as a single impermeable layer at whatever depth, false bedrock can exist in several layers in one location, and these false bedrocks will be resting atop true bedrock.