Interesting specimens you're turning up, you're very lucky! I'd suggest you use sledges and bars to move serious rock. No need to worry about washing stuff down, just move rock where that aqua came from. You may find a pocket, or it may all be crystals locked in matrix. Pressure washing is only practical where you have a nearby source of water and a good pump. You could screen and wash the dirt and gravel, though, that might be well worth doing, and wouldn't take too much water.
When you do find crystals, please try to collect them gently! They're worth more intact, in the rock, complete crystals are what you're after. To make great specimens, don't do too much trimming in the field, bring pieces home and work on them gently with a pressure trimmer or a diamond saw to remove excess matrix. Study the local mines and see what the indicators are, how the pegs trend, and you'll profit from your research. I'd strongly suggest you find out who owns the land. The deeper you go the less weathered and damaged the crystals are. The more blue they are, and the fewer fractures, the more they're worth. Learn what the typical pegmatite minerals are in your area. Don't bother looking for opal or copper minerals; there's tons of info out there on Cali pegs.
You should join a local rockhound club, and ask for advice. But don't show the spot to anybody, unless you want lots of company. If you find a rockhounding buddy you trust, after a few years, get him to help you dig. Two guys with sledges can move tons of rock. If the heat is so bad, collect at night.
And please go easy with the hammer on the crystals, there are many mineral collectors who will go a lifetime without ever finding a gemmy aquamarine crystal!
Good luck.
