You really do make a convincing case, but as you know (or should know )there are people who will remain sceptical to the end. One of those Tunneling machines on earth like the one developed by usaf only on larger scale could create large diameter transparent tunnels through the martian soil. a civilization hundreds if not thousands of years ahead technologically would have no problem with this level of engineering,and this all could have been done 500,000 years ago!