Here is something to consider for the gold cube owners in Nevada/Placer County area. Other threads about buying gravel company sands have shown that
there is gold in those sands. My interest would be to ask whether any mercury is recovered also, as the plant selling this "unwashed sand" is in the mercury
contaminated watershed of greenhorn creek, which flows into Rollins and Combie reservoirs:
Rock Masonry - Hansen Bros. Enterprises
Scroll down to "sand" category and chose "unwashed sand/ pond silt" for prices.