Good, your disbelief does you credit, because the “evidence” summarized is worthless. Taking it point by point:
I’m assuming this is The Golden Road: the story of California’s Spanish mission trail (1962) by Felix Riesenberg, yes?
Without knowing what the incident was, and not finding it through some google book searches, I can’t be sure of the details. That said, there’s nothing sinister about such a find. If the incident is as reported by the book, it’s meaningless - there’s no suggestion that the weapons were Japanese or that they were on an issei’s land or other connection to Japanese-American immigrants. If such a connection did exist, no doubt the author would have found that significant enough to mention.
Further casting doubt on this story, however, is the fact that a Nexis newspaper and wire seach finds no stories of any weapons cache in or near Monterey between 1941 and 1943. I believe the author may have taken rumor and reported it as fact. This is not uncommon in some popular histories.
Doubly meaningless. “Mysterious lights” at sea are not uncommon sights along the shore. Merchant vessels, lightning at sea, temperature inversions causing strange reflections, etc. can all cause “mysterious” lights. They’re only mysterious because the observer doesn’t know the cause and remain mysterious only because this author didn’t bother investigating any of these reports.
In the first flush of wartime paranoia, US forces were sent wild chasing such reports, all with no result. With the steady drumbeat of bad news from the Pacific theater until 1942, it’s no surprise that Californians thought there was nothing stopping the Japanese fleet from appearing offshore any day. This was in fact a common fear.
There was exactly one real incident where the mysterious lights weren’t just wartime paranoia. The Japanese submarine I-17 shelled the oilfield near Santa Barbara, California. Damage was minimal, but it caused an even greater invasion panic along the west coast.
So did European-American farmers, and Hispanic-American farmers, and any farmer at all. As mentioned above, many of these are sited in large, flat areas, which just happen to be great for farming. Oilfields are all over parts of Southern California, and finding a place to settle that’s not near one would be difficult. Futhermore, in California many strategic locations weren’t built until the late 30’s through the early war period - the farmers were probably there first. Again, the author is reporting rumor as fact without investigation and defaulting to the most sinister interpretation possible.
Not as shown by this author. There is the Nihau Incident Gary Baldy summarized, but that’s the only proven incident of Japanese-Americans in the US helping Japanese forces. Although Michelle Malkin has seized on this incident to justify the internement policy and suggested it helped inform the internment policy, the evidence I’ve seen suggests the report on the incident never reached the decision-makers that guided the policy.