One rule: when water slows, the heavy stuff drops
To understand where gold stops in a stream you only need one rule: moving water can carry grains up to a certain weight, and that limit depends on its speed. The moment it slows, it can no longer carry the heaviest grains and lets them go. Because gold is roughly seven times denser than the sand around it, it is part of what gets dropped at the first point where the water starts to slow. Sand and mud travel much further, to where the water almost stops.
Every trap in this section — bend, bar, boulder, junction, bedrock crack, pool tail — is a different form of the same rule. In each, the water loses speed for some reason: the bed widens, the gradient eases, the flow hits an obstacle, or two currents brake each other. When you judge a trap, the question is always the same: why does the water slow down here, and how sharply?
Asking that question is more useful than memorising a list of traps. Every valley is different, and real streams rarely look like textbook drawings. But once you learn to see where the water speeds up and slows down, you can decide where to sample in a stream you have never seen before.
The event that really moves gold: floods
Looking at a clear stream in midsummer and imagining how gold is moving through it right now is misleading. Normal flow is usually too weak to move gold at all; it cannot even shift the coarse gravel. The whole bed only moves during floods: the water rises and speeds up, rolls the gravel along, and gold travels downstream inside that mix, and also sinks deeper through the gaps between stones.
As the flood ebbs, the heaviest grains settle first, at the points where the flood current slowed. Those points do not always line up with today’s low-water channel. A flood usually takes a wider, straighter line than the summer stream, cutting across bends and running over bars. So a bar that sits dry today may have been the inside of the flood channel, and should be sampled as if the water were still there.
To read the flood line in the field, look for its marks: drift piles of branches and debris caught on rocks and trees, a sharp vegetation line on the bank, freshly washed gravel at the edges of the bed. These show you where and how high the flood ran. Judge the traps through the eyes of that water, not the quiet stream in front of you.
Bends, bars and obstacles
On a bend, water is flung toward the outer bank; the outside runs fastest and erodes the bed, the inside runs slowest and deposits. The gravel bar on the inside is where the flood’s load collects. Gold is not spread evenly across that bar: it drops at the upstream end, the head of the bar, where the slowing begins. The downstream tail collects the lightest material, fine sand and silt.
Mid-channel bars work the same way. They form where the flow splits and slows, and any gold again drops at their head, rarely at the sandy tail. Scooping a handful from the surface of a bar is not enough; dig its head down to bedrock or the hardest layer you can reach. Surface gravel only holds what the last flood left.
Large boulders are small-scale traps. A pocket of slow water forms on a boulder’s downstream side and heavy grains settle there; gravel packed under and around its upstream face can be rich too. The best are big, stable boulders that have sat through many floods. Pool tails are worth a look as well: at the downstream end of a pool the bed rises toward the next riffle, the current slackens and drops what it carried through the pool. The churning centre of a plunge pool below a waterfall, by contrast, stirs gold instead of settling it; sample its tail and the cracks at its edge instead.
Slope breaks, constrictions and junctions
A slope break is where a steep stretch of stream suddenly flattens. Water fast enough to carry gold on the steep section loses energy the moment the gradient drops, and leaves its heavy load in the first pool, the first bar or the first bedrock ledge just below the break. It is the trap easiest to see on a map or a profile, and at valley scale it is often the most important.
Valley constrictions have a similar effect. A narrow gorge forces the flood through a small cross-section and the water speeds up; just below, where the valley opens again, it slows sharply. The first bars and bedrock below a constriction are prime traps. Inside the gorge itself the water is usually fast enough to carry gold straight through, holding it at most in bedrock cracks.
At junctions, two currents collide and brake each other, and the combined bed widens. The pool and bar just below a junction, especially on the side where the tributary enters, are classic traps: the tributary pushes its own load into the main stream, the combined flow slows there, and that load lands first on the bar forming on that side. If the tributary drains mineralised ground, its gold ends up on that bar. The best single trap is where these features coincide: a bend right where the gradient flattens. There the water slows for two reasons at once.
Bedrock and false bedrock
Gold is sorted not only along the bed but also vertically through it. As floods churn the gravel, heavy grains work their way down through the gaps and settle as deep as they can go: onto bedrock, or onto the first hard layer that stops them. That is why the richest part of a gravel deposit is often the bottom few tens of centimetres and the bedrock surface itself.
Cracks, ledges and potholes in bedrock are the richest traps a stream has. Direction matters: cracks running across the current, or angled against it, act like the riffles of a sluice and make the water passing over them drop gold inside. Cracks running parallel to the flow let gold slide past. Places where bedrock is exposed mid-channel with cracks across the flow are the exception to the rule of not digging in the middle of the current.
Sometimes what stops gold from sinking further is not true bedrock but a hard layer such as packed clay, cemented gravel or an old lava flow. This is called false bedrock. It holds gold just as real bedrock does, but there may be more gravel, and sometimes an older gold deposit, beneath it. When you hit a hard floor in a hole, it is worth checking whether it really is bedrock.
When you do reach bedrock, do not stop halfway. Once the overlying gravel is cleared, scrape and brush the bedrock and its cracks and pan every scrap. A stiff brush, a thin crevicing tool and patience recover gold that a shovel would leave behind.
- Take every hole down to the hardest layer
- Favour cracks running across or against the flow
- Test whether a hard floor is true bedrock
- Brush the bedrock, scrape the cracks, pan all of it
Pay streaks, terraces and old channels
Gold is not spread evenly across a stream bed. It concentrates in narrow streaks and small pockets and is nearly absent between them. The narrow band where most of it collects is called the pay streak: usually the line the current takes in flood, the inside of bends, and the bedrock surface. That is why two pans a metre apart can give very different results. The way to find the pay streak is to sample across the bed systematically; one large hole only finds it by luck.
Streams do not stay put. Over time they shift their beds or cut deeper into the valley. When a stream cuts down, its old bed is left on the valley side as a flat step above the present channel; this is called a bench or terrace. Terraces are the beds of the same stream from long ago and may have trapped gold by the same rules. Because today’s channel never touches them, any gold in them may never have been reworked.
The same goes for old channels away from the water: a dry, curving hollow across a meadow or a band of rounded gravel on a slope was once a live stream. Because they are not obvious, they are often unworked. Streams that have been worked before should not be written off either; old workings prove a source exists and usually left fine gold, deep gravel and bedrock cracks behind.
Reading a stretch from end to end
Take an example: a medium creek leaves a steep, rocky gorge, flattens at the gorge mouth, bends left a few hundred metres later, and just below the bend a small tributary joins from the left. Three traps stack up in this short stretch. First the gorge mouth: the valley opens, the gradient drops, and the first bar and first bedrock ledge are the first places to look. Then the bend: its inside, the head of the bar on the right bank. Finally the junction: the bar on the left side where the tributary enters.
The water’s behaviour sets the order. At the gorge mouth the flood slows most sharply; coarse grains, and any coarse gold, most likely stay there. The bend catches finer material that made it through that slowdown and is still in transport. The junction brings the tributary’s own load; if there is mineralised rock in that tributary’s catchment, the result there may differ from the other two regardless of them. Sampling and recording each spot separately helps you tell whether gold is coming down the main stream or the side stream.
Much of this reading can be done from a map. Slope breaks, bends, junctions and constrictions show up in elevation data, and GOLDONGO scores every stream segment in a region on exactly that geometry. What a map cannot show is bedrock cracks, individual boulders and the current state of the gravel. That part is done on foot, and no geometry puts gold into a catchment that has none.
- Find where the water slows, and why
- Work out the flood line from flood debris
- Sample the head of bars, not the tail
- Take and record a separate sample at each trap
- Note what each tributary drains