New seismic-reflection profiles image the crustal structure of the Beaufort-Mackenzie basin and adjacent features near the Mackenzie Delta in northwestern Canada. The Mesozoic to Quaternary sediments are nearly 12 km thick under Richards Island at the edge of the Beaufort Sea and are bounded by listric normal faults on the south edge of the Beaufort-Mackenzie basin. These faults parallel features that are Proterozoic in age; this suggests that the older features controlled the younger. Thrust faults are identified from offsets in reflections from Proterozoic strata underlying the Campbell uplift. The age of the compression is not yet clearly established; it may be either Late Proterozoic or late Paleozoic. A Late Proterozoic age would imply that Precambrian compressional structures underlie much of northwestern Canada. A late Paleozoic age would imply that Ellesmerian (Devonian–Carboniferous) compressional structures are buried beneath the Arctic coastal plain from the Mackenzie River delta to the Parry Islands fold belt, some 1000 km to the northeast in the Arctic Archipelago. The base of the crust is imaged on the south end of the profile at approximately 39 km, whereas in the north it is inferred, from gravity modeling, to be at approximately 28 km.