I am by no means an expert, but having just seen a bunch of these at a pirate museum, it looks real (reale???) to me. After a little searching, it is an 8 reales cob coin (the 'Pillars and waves' variety) minted in either Peru or Bolivia by the Spanish. There is also a very nice clear date on it of 1763. If it's real, the weight should be around 25-27 grams, so I would suggest weighing it! Cool find for just playing on the beach regardless!
Modern reproductions of these coins, fakes, are sold by the thousands in tourist traps and greatly outnumber the genuine coins. And yes, it's quite common for people to just throw them away on the beach. Sometimes after being fooled by them (the fakes) themselves.
Before I would condemn them as phony I would do a weight test. I cannot tell the size from the pix but if you research the weights of the various denominations, one real, eight reales, etc. you might be able to better establish their authenticity. A California beach might sound a bit odd to Pirate money fans but remember that California was Spanish long before it became a part of the US.
Hello aod626, One very quick check is to see if it is attracted to a magnet. There is probably a magnet on your electric can opener that will allow you to perform the quick test. See if it is attracted to the magnet & report back here. You have your sandcastle find in a nice plastic flip. Where did you get that nice plastic flip?