Books in Sun series

Sun Catcher and her mare, Sunshine, chance upon Stubborn Echo, a boy from her tribe who has stolen the big wind-drinker, Ghost, away to ride. Nearby, a grizzly bear cub emerges from the trees, it's massive, protective mother right behind it. Sun Catcher and Echo race the wind-drinkers through the forest to escape the bear, and suddenly, the ground gives way. Echo and Ghost plummet into a black pit! Sun Catcher sets out to rescue them, but she's forgetting one thing: Echo detests her. Will he abandon her in the darkness?