North of Grand Rapids, Manitoba, new exposures of a carbonate succession prompted study of the lithology and paleontology of the uppermost Ordovician along the northern edge of the Williston Basin in Manitoba. Modern concepts and approaches were applied in examining the sedimentary rocks and fossils, including X-ray diffraction, stable carbon and oxygen isotope analysis, and statistical algorithms. Nine lithofacies, representing a series of shallowing events, and environmentally significant subaerial exposure surfaces, were identified. The distribution and relative abundance of identified fossils were used to delineate faunal associations, which were examined in the context of the impending end-Ordovician mass extinction. Historically, the stratigraphy of the latest Ordovician has been problematic. Therefore, detailed examination of this succession aided in clarifying unit boundaries in the Stony Mountain and Stonewall formations. Study of this new succession contributed a wealth of information to the understanding of the uppermost Ordovician of Manitoba.