The Mackenzie District of the Northwest Territories composes the western part of northern Canada addressing the Precambrian, Paleozoic, Mesozoic, and Cenozoic geologic history. The Mackenzie District starts with a discussion of the Snowbird Tectonic Zone, the Southern Rae Craton, the Taltson Magmatic Zone, Central, Western, Northern, and Northwestern Slave Province. The Wopmay Craton is discussed before moving into the Proterozoic and Phanerozoic sedimentary cover in the Mackenzie Platform and Macdonald Platform areas. The sedimentary cover section focuses on the northern basins and platforms. Paleozoic cover from the Cambrian through Permian Periods, the Mesozoic Era periods, the Cenozoic Era periods including a brief discussion of the Western Interior Seaway as it related to transgressive-regressive cycles, and the Quaternary Period glaciation ending with the Holocene Epoch are included. The many publications produced by the Geological Survey of Canada contributed toward the contents of this book and are referenced.