Though virtually unknown before 1851, the exceptionally scenic Yosemite Valley of California soon attracted continuing attention as a geological anomaly. J. D. Whitney, state geologist and Harvard professor, advocated a tectonic theory of its origin. Despite its seemingly official status, Whitney's theory even failed to convince some of his own subordinates. An unexpectedly effective dissenter not associated with Whitney was John Muir, then a tatterdemalion vagrant. Though the two men never met, conflict between their inflexible and mutually exclusive geological theories persisted well into the twentieth century. Eventually, both dogmatists were proved wrong, but Muir had come closer to what we now accept. Several geological and geomorphological issues of importance entered into later discussions of Yosemite. The whole controversy, moreover, illuminates such further issues as the influence of preconceptions on theorizing, the role of authority in science, and the interactions of professionals with amateurs.