Excellent information for new prospectors.
Ancient river beds can be either high benches or old river channels that are now overgrown with cottonwood trees and other water loving plants.
Picture of a cottonwood tree and green reeds growing out of an apparent dry area. A hidden submerged old waterway lies underneath.
Just let me say there is a lot of gold still waiting to be mined out there. When you look at the geological history of our earth and all the glacial movements of massive gravels, sands and mountains, it is not hard to understand that there is still a large quantity of placer gold "in them thar hills". The best indicator of gold, or gold bearing deposits is any low spot or river valley that cuts through any area of land. Usually we concentrate our efforts in these wet low drainage basins. This is the "easy gold", but this easily mined gold only represents a small portion of what is really available. Rivers (or streams) cut through ancient riverbeds which through time are sometimes left "high and dry" (high benches) on their journey to the the ocean.
Obviously finding ancient or orphaned valleys that contain decent if not large quantities of coarse gold is very lucrative. The richness of these areas makes finding them very worth while. This is especially true if an area has been well worked.
Two Things to Look For
A river or stream will change direction many times through it's life time.
These somewhat obvious old river channels are often rich in gold deposits as well as other minerals and gems. What I look for is an overgrown gravel area with cottonwood trees growing on top. Cottonwood trees have a relatively short life (60 - 100 years) and their roots will naturally seek out "wet pockets" on bedrock. During dry periods (August) look for the trees with the greenest leaves. These trees are pulling water from the deepest pockets in what appears to be a dry area.
The second strong indication is bedrock and large boulders that have been worn or smoothed by water. I look on the valley sides or banks for large sheets of bedrock that extends downwards on an angle into what was once the river or stream.
These large sheets of rock ar like nature's finger pointing the way to riches at the hidden bottom. When you use the combination of trees and bedrock as indicators for gold, you stand a very good chance of hitting some very rich pockets.
A high bench is basically an ancient river or stream that has been left high up on the side of a valley. Sometimes these high benches can be obvious, other times not.
What to Look For
Look for pockets of green growth, trees or bushes in an otherwise dry area. This is the easy way to find placer gold in these elevated locations.
I was first made aware of this method by an old prospector that worked a gold claim in Atlin, B.C. The grizzly old miner had a full beard and mustache stained orange by his pipe smoking. He would often gesture with his pipe, pointing out different parts of his mining operation. Once, just after a meal, he pointed to an especially green patch of aspen and cottonwood trees growing about 1/4 mile up the hill from his claim and said "That's where the real gold is". He went on to describe why it was an excellent location and if that were part of his mining claim, he would start digging there looking for nuggets. The spot was a "v notch" upon the side of the mountain. Once side of the notch was a huge slab of bedrock (a massive flat rock), while the other side was an assortment of fist sized rocks. This tiny valley went back about 50 yards into the mountain before stopping and continuing upwards again. Everything around that spot was drab and lifeless except that location, which was full of green trees and other plant growth. He described how to dig along the bedrock, from the exposed portion down into the ground. He said "you look for a sudden change in soil density - clay or a hard rock bottom". As you are digging down, you keep taking samples. Pan out these samples looking for black sand, fine gold and in this area, garnets. When you hit a rich spot it will be obvious. Your sample suddenly has gold pieces in it. Dig a little further and you are into nuggets.
Once you have found this, clean out the spot with special attention on the bedrock cracks. These cracks will contain the richest gold deposits that can not be easily washed away. Continue digging back into the bank until:
a) all the gold runs out
b) the overburden becomes to great to keep going.
That sounded straight forward until he told me I couldn't go up there and dig for gold because it was off his claim. Yes, I was very disappointed.
Some good advice from an old prospector.
Most of us know the basic idea behind Ancient Riverbeds, old dry rivers that contain good quantities of gold now, we just have to know how to find them.
Some Common Rules to Help You
- Most ancient dry waterways will be higher than the current stream or river. (This includes when the river changes course).
- Are the valley sides made of just loose gravels and rocks or is there bedrock or the solid rock of the hills and mountain present?
- Has there been any hard rock gold claims in the area?
- What size of coarse gold nuggets have been found? What quantity?
Since a river wears it's way into the valley floor, pretty much all older riverbeds will be higher. Sometimes much higher.
The reason the valley sides are important is that any solid rock will hold an elevated riverbed intact for millennia. Gravels, silts, sands are usually glacial wash down and may contain gold but it is not the source of it.
If there are hardrock gold formations nearby the odds are that that was the source of gold in the area. It is time to stop looking for the ancient riverbed and look for other gold formations. Keep in mind that outcropping of gold (intrusive rock formations) occur in clusters.
Picture a main vein of gold being broken into fingers. These fingers fan out towards the surface. The "found gold vein" is quite possibly an offshoot from the main vein. When searching for ancient stream beds always be on the look out for rusty, oxide stained white quartz formations. This quartz normally is sticking out from the ground because it is quite hard. It is harder rock that the surrounding "parent rock" that it went through to reach the surface. Ancient river channels are often easy to spot once that material is exposed.
1) The lower sections of these riverbeds are often comprised of cemented gravels that when freshly exposed are blue in color. This blue cemented gravel turns a rusty reddish brown when left open to the elements. In this case, look for loose soils, gravels and sands surrounding a "blob" or outcropping that is:
i) rusty in color
ii) appears to be a cemented mass.
Take samples of this gravel "blob" at different locations. You are looking for black sand and fine gold. Use your gold pan to test these gravels.
2) These ancient river channels are often, but not always, located on bedrock. A perfect example of what to look for is:
i) a shelf of rock or bedrock off the valley floor with something somewhat solid sitting on top.
ii) the gravel / sand part sitting on top of the bedrock will be:
a) dark brown
b) rusty brown
c) blue (if freshly broken)
iii) The black color indicated magnetite and other oxides present in the lower layers of the riverbed. As always, take samples and pan the results. You may have to crush or break apart a sample. Look for high concentrations of black sand and fine gold.
The Cheat Method
Take a strong super magnet and run it over the cemented gravel near the bottom where the rock shelf or bedrock is. If you have found a potentially good spot, the magnet will quickly be covered in black sand (magnetite).
This cheat method also works well in desert areas and deep pools at the bottom of waterfalls.
Another Effective Way to Find Ancient Riverbeds and Channels
Using the existing river or stream as a fixed starting point, work your way along the bank taking samples as you go. We want to focus our samples on natural depressions and rock shelves. Identify each sample taken making sure to mark, on each bag, the location it was taken from. Work up the sides of the river valley always sampling from low natural depressions or any type of rock shelf. When you have taken all the samples you want, use a gold pan to check the results. When you find indication of an ancient waterway (black sand and fine gold), return to that spot and take many samples in a wide pattern. If you plot your heavy concentrates on a map you will quickly get a "birds eye view" of where the old river was.
Work you way up the hill or mountain taking samples in approximately 100 yard widths up past where you think the ancient river might have been. Once more, pan out the concentrates. What we are looking for is where the heavy black sand / gold samples thin out or stop. This will tell us the height or elevation where the river channel was.
Finally we start probing the gravels looking for a denser section. We might find bedrock or rock shelves, but we will find things that aren't suppose to be there. Among natural broken mountain rock and associated debris you may suddenly find water smoothed gravels and different colors that don't match most of the mountain's decomposing rock. As I already mentioned, there should be a denser section of concentrates or cemented gravels.
The reason you will tend to only find very small heavy concentrates while looking for the ancient riverbed is that most of the larger heavies quickly sink into the mountain's natural rock (slide). Using a pry bar and a good shovel, work loose the concentrates on the lower section. Check for coarse gold (nuggets).
Make sure to also break up and pan out other sections of this gravel mass. These hardened sections occur in bands and there may be some very rich gold finds suspended in the upper gravel mass.