There are cave paintings/petroglyphs at 3000m above sealevel in the valleys of the Andes, central Asian mountains and Tibet (and probably more I don’t know about). I dont think there is enough water on earth, ice or otherwise for 3km sea level rise.
You want to store information for eons? Build it in to the ratios of a pyramid. Then no one will ever figure it out. Or at least there will be a huge disagreement as to what you meant.