Common riffles are merely pieces of wood extending from one side of the trough to the other.
These form obstructions which impede and collect the gold. Common riffles vary in size, depending upon whether they are used in a rocker, Tom, sluice or dredge. Zig-zag riffles are similar to common riffles, except that they do not extend all the way across the trough. Instead, the alternate ends are open, forcing the water to swing around them like the curves of a stream. Some pioneer prospectors swore by this type of riffle, claiming that it was the most efficient for recovering the finest values.