(I need a good geology course)
I remember back in college hearing that somebody was a geology major.. Why

Who the heck wants to look at rocks?? Being an accountant sounds more
exciting... Fast forward 20 years and I wish almost everyday that I was a geologist..
just a shovel full right on the surface.
I've sort of mostly found the same thing.. And back to the geology thing, apparently over the past 30-70 million years or something like that, the entire area
has eroded down about 1000 feet.. There is outcropping there, and an outcropping there.. Little bit of green rock here, and a little bit of green rock there..
The vein at some point was above my head.. Sweep the top couple of inches, and there is gold, just sitting on the hillside.. Dig down 4 inches and there is
nothing.
Toss in an arroyo that may only be a few hundred years old, concentrating all that gold sitting on the surface (and maybe digging into some older
deeper stuff along the way), and from what I've experienced in Hillsboro, just like you, the best stuff seems to just be sitting there on the top.
I've TRIED to get skunked just taking dirt from spots that shouldn't have ANYTHING, based on conventional gold reasoning.
I've found some reasonable gold with that method.. I even swept the dust off a dirt road one time, just to see, and sure enough
there was gold in it.. Not a lot, and not big, but I got gold sweeping a dirt road and taking half a bucket.
I think its a fascinating area, the history, the old buildings, the mines.. The geology, at least what I can understand of it... Lot of fun.