UPDATE: Sitchin is discredited.
I've just listened to this interview of Zecharia Sitchin. It's in 12 parts so you'll need to work your way through it and also if anyone wants an electronic pdf of his books there are plenty available on the net if you don't mind digital scrumping action.
Perhaps the Nephilim had the technology to do the relief 'printing' on hard stone as used in the video above. Maybe they took that technology with them when they left their lieutenant bloodlines in charge at the time of the last flood.
The Darwinistas might want to research points like that if they weren't still slugging it out with Genesis peddlers.