Where to Dredge for Gold
Looking at the “hydrology” of a curve, the water flowing at the outside of the curve is moving much faster than the water flowing at the inside of the curve. Therefore, the water pressure at the inside of the curve lessens and the water pressure on the outside of the curve increases.
As the gold continues to be pushed down river, the gold that is farthest to the outside of a curve is pushed around the curve. That gold that is closest to the inside of a curve will tend to drop where the water begins to slow down at the beginning of the curve. This is also a good spot to look for gold.
As stated earlier, gold being the heaviest of the materials in a river, combined with the agitation of all of the materials in the river at flood stage, will drive the gold to the bottom. The bottom of the river is bedrock. The bedrock may be shallow, and have very little “overburden” on it (or even be exposed), or it may be deep (30 or 40 feet or more under the overburden). Since the gold will be resting on the bedrock, you must be able to reach bedrock where you are dredging. Keeping all of the previous criteria in mind, look for an area that has bedrock shallow enough for you to work.
A clue to the depth of bedrock can be seen on the banks of the river. Exposed bedrock on the banks will indicate that bedrock is shallow. Exactly how shallow will not be known until you actually begin dredging. Sharp drops in the bedrock on the banks may indicate a continuation of that steep drop underwater, meaning the river bottom may be quite deep. A gradual drop in bedrock at the banks means just the opposite. That bedrock is probably fairly shallow.
Remember that these are “Rules of Thumb” and do not always work in all cases.
If no exposed bedrock can be seen in the river or on the banks, look up on the sides of the canyon. Look for an outcropping of rock on both sides directly opposite of each other and draw an imaginary line from one outcropping down to the river and then up to the opposite outcropping. Where this line crosses the river is a pretty good indication of where the bedrock will be the shallowest.
The bedrock at the bottom of the river is not the only place you will find gold, however. When the bedrock is deep, there will be clay layers that form at intervals from the river bottom to bedrock. When compacted, these clay layers can act as a “false bedrock.” That is, unless the flood is sufficient to churn up the entire river bottom all the way to bedrock, then the material in the first few layers may be all that moves. The gold may be heavier than the material in the clay layer, but unless that material is agitated, the gold can’t penetrate it. So, the gold will be sitting on the clay layer, or may only penetrate it as far as the overburden will press the gold into it.
As a rule of thumb, the gold will be in about the top 6 inches of the clay layer. If you dredge beyond this top 6 inches, be prepared to go to the top of the next clay layer (or bedrock, whichever you reach first).
Clay layers will vary in thickness from a few inches to several feet thick. So going to the next clay layer can be quite time consuming. The dredging hole must be expanded to go deeper so as to make removing boulders easier and working in the hole safer (from cave ins).
When working in an area that you know will have clay layers, consider each clay layer “bedrock” and work it like you would bedrock. Once you reach it, work laterally (to the right and left) until you reach the outer edges of the pay streak. Once the sides of the pay streak are found, you must decide whether to continue on this layer or dredge down to the next layer. But, when making your decision, remember that just because there is a pay streak on this clay layer does not mean there will be a pay streak underneath it on the next clay layer. There may be a pay streak on that next clay layer directly underneath the pay streak of the clay layer your working, but, it may be located to the left or right , or may not be present at all.
Working clay layers can produce good gold, but the best gold will be at bedrock. Try to work areas where you will be able to reach bedrock immediately, or at least only one or two clay layers before bedrock.
As stated previously, gold only moves when the water pressure is high enough to move an object 19 times heavier than itself. So when the water pressure lessens, even a small amount, gold “drops.” So, let’s take a look at some conditions that will decrease water pressure of a river during its flood stage. Doing so will provide a short list of locations that gold will tend to collect, or “pocket.”
We already know that the inside of curves is a good place to look for gold. Both the point where the inside of the curve starts, and the fan or “pay streak” after the curve will both have good gold. This is because the speed of the water at the inside of a curve is less than the “mean water speed.” We also know that the speed of the water on the outside of the curve is greater than the mean water speed. So, no gold (generally) will be found on the outside of the curve, as the water pressure has pushed it around and out of the curve.
What other conditions can cause water speed to slow down, or “break?” Any large object in the water will have that water “curving” around it. And, just like a large curve in the river, the water that curves around an object will have gold deposited at the beginning and ending of those curves.
Consider a large boulder sitting in the river. Water flows around the boulder. The water “curves” around the boulder on both sides. If you look closely at the center of the upriver side of the boulder, you will see that the water is almost stopped. That is a place that gold may pocket (at the center of the upriver side of the boulder. If you watch the water as it curves around both sides, you also see a location where the water again almost comes to a stop, and that is the center of the down river side of the boulder. This is also a good location for gold, and is generally better than the up river pocket.