The distinctive, branched thrombolite, Favosamaceria cooperi new group and form, is found widely in the Great Basin, USA, where it is restricted to the Late Cambrian Saukia trilobite Zone. This thrombolite is distinguished by a hedgerow, mazelike organization of ridges similar to garden walls (maceriae) in plan view, branching of ridges into daughter ridges and columns, the polymorphic nature of dark, 1–4 mm mesoclots, and the relative consistency of maceria width (approximately 1 cm). As a group, Favosamaceria is found elsewhere in Upper Cambrian strata of the Argentine Precordillera, Appalachians, and Upper Mississippi Valley, as well as in Lower Ordovician deposits of the Canadian Arctic and Newfoundland. The distribution of the group around Laurentia illustrates the use of microbialites in biogeographic studies.