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West of Fiambalá, the paved road winds through the high desert, past picturesque red rock escarpments known as the Quebrada Angosturas, and into some serious altitude, topping out at the Chilean border. It's a stunning drive, with no services apart from a seasonal white-elephant hotel halfway between Fiambalá and the frontier. Los Seismiles are the peaks above 6000m, and you'll see several of them, including Ojos del Salado (6879m), the world's highest volcano.
The transition from desert into the high country is mind-boggling. You'll glimpse glacial streams and icy wetlands teeming with flamingos, yellow tundra home to grazing vicuñas, and then finally the spectacular Seismiles will appear from behind still other snowcapped peaks. During the summer the road is open all the way to the border, but at all other times of year, the road is closed at La Gruta, an Argentine border post 21km from Chile; a precaution against inclement weather on hazardous roads that can be icy and dangerous thanks to gusts of viento blanco (white wind) that may blow in at anytime.
Even more awe-inspiring scenery is accessed via a lonely (4WD-only) mining road that leads 90km to Monte Pissis (6793m), the Americas' third-highest peak. It's about five hours return (50km) to a viewpoint over this imposing mountain, with hauntingly beautiful blue, black and turquoise lakes in the foreground. Due to its isolation, this is best by tour; operators in Belén and Catamarca can make arrangements.