Re: Grasping at water straws
"To establish a colony on Mars we'd first have to send the shielded structures for people to survive in while they assemble the machinery needed to excavate the sub-surface habitats - that's a lot of very heavy stuff that has to be got from Earth to Mars."
Or we could land at existing caves, and set up temporary shelters inside them whilst we build the permanent ones.
Take Olympus Mons, for example. Huge, HUGE, volcano, riddled with caves and tunnels.
Find an underground dome about 1-2 km across, preferably near the top for ease of getting on/off the planet (Did I mention that it's HY-UUUGE?), and set up a habitat in there for long term, or use smaller caves for short term outposts for exploration.
Natural rock shielding from solar/cosmic radiation, plus insulation from cold.