Seismic reflection profiling in the Purcell anticlinorium of southern British Columbia, Canada, using a land air gun source, has revealed reflections from depths of at least 15--20 km. Interpretations of these data, in conjunction with related geological and geophysical information, confirm the allochthonous structure of the Purcell anticlinorium and suggest that autochthonous North American basement at 15--20 km depth beneath the anticlinorium has a westward dip of 15¿--20¿. The thickness of the crust above the North American basement surface may be accommodated by structural repetition of Purcell strata, by thrust slices of North American basement rocks, or by both. The geometry observed on the reflection data implies that the Purcell anticlinorium is cored by a crustal-scale thrust anticline (hanging wall anticline). Further, the data demonstrate that land air guns are effective sources for crustal reflection work.