THE LEATHER THRONE by Owen Ulph (Dream Garden: $19.95). Though billed as a "nonfiction novel," this sprawling account of a year in the life of a Nevada ranch hand is as hard to brand as a cornered bull. Owen Ulph, a retired professor of European history who worked three years as a cowhand in the early '50s, writes of obstinate cows, cantankerous cowboys and a vast slab of rangeland in what amounts to a reminiscence: one man's giant mural of a vanishing way of life. This is not Marlboro country. Life in the saddle is usually tedious, and Ulph's real-life cowboys become increasingly confused and threatened as modern ranching makes their skills outmoded. While authentically gritty, Ulph will leave all but the most rugged reader behind in dense thickets of detail, in gusty canyons of philosophizing. "What principle," he writes of hunted creatures like the jack rabbit, "serves as pilot when the choice is between holding one's slender existence in specious abeyance or exposing it, through flight, to dangers which, if ignored, might remain in the unbegotten?" Yet, packing a saddlebag of memorable anecdotes, this book at its best captures the poetry and the vernacular of a bittersweet life and the men who watched it die.