Massive dolomites, hosted in the Cambrian-Ordovician of the southern Canadian Rocky Mountains, form strata-bound sheets over broad platforms, except near the margin, where they also form dikes that crosscut sedimentary bedding planes. Field evidence indicates that the two kinds of dolomite bodies were formed by pervasive, formation-parallel flow and fracture-channeled, cross-formational flow, respectively. Fluid-inclusion data indicated that the primary dolomitizing fluids were warm to hot (100 to 200 °C) saline brines (13–25 wt%). The timing of dolomitization (Silurian to Late Devonian) coincided with the timing of the early Paleozoic contractional deformation in the west. Finite element modeling showed that the observed dolomite geometry and geochemistry are consistent with miogeocline-scale ground-water flow driven by west-to-east topographic relief.