The conquistadors called it the desierto -- a simple synonym for the altiplano, the high plateau of their Spanish homeland -- but the Yankees saw the desert as a wasteland, an arid expanse of sun and sand inhospitable to every form of life. Actually Kirk, author of several juveniles and guides to our National Parks, reminds us -- if we don't already know -- that desert country contains one of the world's most varied and delicately balanced ecosystems, its harshness ""underlain and intermixed with harmonies."" The Sonoran Desert, which extends 250 miles into Mexico and includes southern Arizona and most of Baja California, is an area of lowlands and mountains, canyons and gorges, arroyos and stony desert pavements. Here one finds the ubiquitous mesquite and the localized saguaro cactus (the Sonora is the only place it grows), rare Boojum ""trees"" (""Boojums are mysterious THINGS. . .neither wholly animal nor simply plant,"" according to Lewis Carroll), gila monsters (""the slowest crawl in the desert"") and rattlesnakes, peccaries and pocket mice, road runners (""a digestive tract encased in feathers"") and owls. Kirk's approach is biologic rather than anthropomorphic; she emphasizes natural phenomena (wind, rain, temperature) and processes (reproduction, hybernation and estivation, photosynthesis). In taming the desert we are in fact destroying it and this book, part of the ""American Naturalist"" series, is a plea for its preservation. Less personalized than Krutch's Desert Year, but an educative guide to a fascinating world.