El Dorado.
No, the question is how useful they will be to colonists, and how much effort it will take to develop them.
We cannot let our limited knowledge of these formations be used as a justification for
an extremely expensive program that may not go anywhere.
Remember all those golden cities and friendly natives ready to be converted to
Christ that were used to justify the conquest of the New World?
And there are lava tubes in Hawaii, too, but no one's putting condos in them.