Rider at the Gate by CJ Cherryh

As a one-sentence over-simplification you could describe Rider at the Gate as a kind of dark fantasy Western on a frontier planet with three-toed telepathic horses. That description will probably tell you whether or not you might be interested in the story, but it doesn't do the novel justice. It's about loyalty and secrets, family, hardship, and the difficult lesson that people can be complicated creatures with tangled motives.

Danny Fisher is an awkward teenager, town-born but lately chosen as a Rider by the young nighthorse whose self-image is best translated as Cloud. He's all set to spend the winter in the Rider camp adjacent to his home town, where he can visit his God-fearing (and hence Rider-hating) family regularly for an uncomfortable shared meal, but it won't necessarily be that straightforward. Reports arrive of a horse gone rogue; rogue horses can project images further and stronger than the others, catching everyone unawares and if they're not careful, driving them to insanity or death. Danny gets caught up in a situation he isn't prepared for, but the trail on the edge of winter isn't the most forgiving place for a junior to make elementary mistakes.

I've read a few CJ Cherryh novels now, and been consistently impressed. Rider at the Gate was an easy read, laced with dry humour and well-drawn characters, including the nighthorses who each had unique personalities. The world was vividly conjured, from the snow-covered mountains of the High Wild to the poisoned industrial landscape further down, and the truck convoys the Riders are paid to protect. With the scattering of technology (diesel-powered trucks, phone lines strung alongside mountain passes) this is a bit grubbier and more down to earth than a lot of the more rose-tinted fantasy novels you might expect to involve horses, mountains and a quest, but I would say it's more likely to appeal to the fantasy-reading end of the SF spectrum than the hard sci-fi crowd. There is an equally-enjoyable sequel called Cloud's Rider.