Those rocks looked man made to me. If the area was a former Japanese camp during WWII and if you can have a good downer check it, maybe you can find the dig site (most probably near the "X"). Then you can do a little digging during your spare time and who knows? That's how a group of TH that I knew found their fortune. But be sure you use your head and not your heart if you decide to dig. And never quit your job, just do it on weekends. And maybe later you can find a financier....