Follow The Wind by Don Coldsmith, (Spanish Bit Saga Series, Book 2) from Books in Motion.com

Don Pedro Garcia believes the drunken Captain Sanchez' claim that the Don's only son is still alive and living among the savages in New Spain's uncharted wilderness. The Don makes Sanchez his guide on an expedition to find the young man. Lieutenant Ramon Cabeza, a true soldier and friend to the Don, mistrusts this new so-called guide and discounts his wild tale of a hair face living among the native peoples. The mystery widens as the expedition continues, for no matter how quickly they travel the natives always seem to know their plans and movements in advance. Someone is shadowing the expedition as it is caught between the wars of the Head Splitters and The People. Someone who knows them and their ways too well.