I have seen many samples taken originally with an eye toward getting the highest grades possible, but later someone claims that those results represent an average grade of the whole gravel deposit.

The design of metal detectors well-suited for prospecting is an interesting process and not necessarily an easy one to achieve. It is a combination that blends the desires of what prospectors would like, the requirements of sales people and dealers, with the science and physics of what the electronics can achieve.

The old timers typically washed these areas down to bedrock, and some areas appear terraced. I would imagine this is because these hydraulic mines were generally where the miners found old Tertiary river channels on the sides of mountains that were gold-bearing.

What do you do when you’ve located a promising deposit of gold or gemstones, but it’s trapped in solid rock?

Rivers are not just random and accidental; streams and other drainages are what they are because of the forces of erosion acting on the bedrock.