De Beers (not "Da Bears") has a large supposedly industrial diamond reserve south of Trinity County in Butte County at the old Gold mining site of Cherokee which by the way Thomas Edison was a stake holder in. A little closer, in Tehema County there was an old hermit cowboy who in the 50's if I remember the time frame correctly used to come into Red Bluff and pay for his goods with diamonds he was supposedly finding nearby. An old friend of mine who knew the old timer knew where the man had his camp and spent years looking for diamonds but never found any himself. If your familiar with the area the drainages are full of localized areas with huge Basalt chimneys. Basalt Chimneys are supposedly made under pressure the same as diamonds so I suppose it makes sense. A hint of where his camp was for those that may know a little bit of local history- He lived in an old horse trailer that once belonged to movie cowboy Tom Mix. The trailer was finally removed in the late 90's or early 2000's when they made the area into an official campground. Sadly the outhouse now sits exactly where the trailer sat.
Another related story to that same exact area, which is not a known gold producer, was a supposed lost exposed gold vein found by a man from Vina who was making his way to Reno or Susanville. He found the vein and planted his axe in a tree to mark it then continued on his journey. He was never able to relocate it and no one has ever claimed to find any gold there.