These books give an incredibly realistic account of the terraforming [areoforming?] of Mars in the mid 21st century. Written in the early 90's the details may be passed by recent Rover and other explorations, but the vivid sense of place amid the weird geology of the red planet makes this trilogy continue to spark thoughts days and weeks after reading it. I used the National Geographic maps of Mars as a reading aide, but found that I started thinking of Mars in terms of Robinson's books, and not just as a fictional construct.

Like all great science fiction, the hard science is matched by the explorations into human existence, in this case, following the attempts by many of the 'first hundred' Martian settlers to opt out of the cycle of capitalism and global exploitation that at the time of the books, sees the earth searching desperately for resources off planet.  Various forms of anarchism and communalism are attempted,  hampered always by interference from the global transnationals that run earth.  Red, Green and Blue take on vivid and metaphorical significance as the factions vie for control of the planet. 

From Green Mars:

The land they were crossing now was dominated by crater rings, the newer ones overlapping and even burying older ones. "This is called saturation crate ring. Very ancient ground." A lot of the craters had no raised rims at all, but were simply shallow £latbottomed round holes in the ground. "What happened to the rims?"
"Worn away."
"By what?"
"Ann says ice, and wind. She says as much as a kilometer was stripped off the southern highlands over time."
"That would take away everything!"
"But then more came back. This is old land."
In between craters the land was covered with loose rock, and it was unbelievably uneven; there were dips, rises, hollows, knolls, trenches, grabens, uplifts, hills and dales; never even a moment's flatness, except on crater rims and occasional low ridges, both of which Coyote used as roads when he could. But the track he followed over this lumpy landscape was still tortuous, and Nirgal could not believe it was memorized. He said as much, and Coyote laughed. "What do you mean memorized? We're lost!"
But not really, or not for long. A mohole plume appeared over the horizon, and Coyote drove for it.
"Knew it all along," he muttered. "This is Vishniac mohole. It's a vertical shaft a kilometer across, dug straight down into the -bedrock. There were four moholes started around the seventy-five degree latitude line, and two of them are no longer occupied, even by robots. Vishniac is one of the two, and it's been taken over by a bunch of Bogdanovists who live down inside it." He laughed. "It's a wonderful idea, because they can dig into the side wall along the road to the bottom, and down there they can put out as much heat as they want and no one can tell that it's not just more mohole outgassing. So they can build anything they like, even process uranium for reactor fuel rods. It's an entire little industrial city now. Also one of my favorite places, very big on partying."