I just love that Grand Canyon/Egyptian relics story! Seriously! I think Stephen Quayle had a story about bones of giant men being found there too.
Aside from that, alien/ufo encounters may have been recorded as much different things in the past -- fairies, demons, angels, so on. So it may be hard to tell what was an actual alien/ufo encounter because they have become part of the folklore of beings and events that we don't think of as being aliens or ufos.