Restless Spirit (Te Wairua Whakariuka) by Susan Brocker is the story of Lara, Kahu and a wild Kaimanawa Stallion.
The book follows the white stallion from the time that he was a small colt. From that time, he was hunted by humans who wanted to capture him due to his beauty. He is extremely elusive, though will search for a palomino mare that he found years ago, though she was captured and sold along with her own colt. When the white stallion is captured, Lara and Kahu must figure out how to set him free - though they face the fact that, to help him, they may have to lose him.
Kaimanawa horses live in the Kaimanawa Ranges of New Zealand, near the town of Waiuru, near the Waiuru Army Base. This book is pretty accurate to the real details - what the ranges are like, how the horses live.
Near the start, the book also mentions the stallion, as a colt, throwing himself onto his side and sliding to escape a helicopter. Kaimanawas have been known to use this method to slide across swamps to escape helicopters - one woman has a very real story of how, after a lot of rain, her domesticated Kaimanawa mares slid down a hill in turn, destroying that part of the paddock.
This book, though a great read, is probably for 12+. Some parts may scare or upset young children.