"To the Memory of the Unknown Dead"

This confusing stone in Mt.Vernon says there are unknown persons buried within range of posts, but we saw no posts. And who are these unknown dead? From a specific tragedy? Or do all unidentified "John Doe" bodies get interred here?

Anonymous Cross in Oakdale Cemetery

This homemade wooden cross with no inscription is near the front entrance of Oakdale Cemetery in Irvine. Possibly an unknown soldier, or just a general monument to all unknown soldiers?