You did not say how deep it was, or how large the gold is that is found. If your material is more than a couple of inches and your gold is small then a VLF is a waste of money, if your material is say 10 or 12 inches to hard pack and the gold is on average of 4-5 grams then a VLF could be a choice, but unless you live in Northern CA or Australia, that size gold is scarce.
Most large washes I've seen(in southern AZ) there is little bedrock, the sand is 3-10 feet, if that is the case you need a backhoe.The average wash I look in is 2-3 feet wide there the bedrock might still be at 10 feet but there is a clay layer at 10-12 inches. I've found a couple of 4-5 gramer's, usually at 6-8 inches in clay or hard packed red dirt, most of the gold that is found is sub gramer's. Buy both a PI and VLF cover your bases.
As you go north in AZ the bedrock is shallower, southern AZ=deep, if you are unsure of the area you are going to prospect either find the geological reports or spend a day with a #2 shovel