A 250-km-long east-west geological and geophysical transect has been constructed at about lat 66°40′N, from near the Yukon-Alaska border, across the Eagle Plains foldbelt and Richardson Mountains anticlinorium, to the Interior platform in northwestern Canada. It includes reprocessed industry seismic reflection profiles, regional gravity data, and drill hole information. The north-trending Richardson Mountains anticlinorium is interpreted to be a contractional (pop-up) structure, having a core of Proterozoic and lower Paleozoic rocks; the structure is bounded on the east and west by post-Early Mississippian, pre- or syn-Cretaceous thrust faults. Contractional deformation in the Eagle Plains foldbelt is probably the same age. The location of the pop-up may have been controlled by a preexisting west-facing crustal scale ramp at the top of the crystalline basement. A horizontal displacement of about 33 km is required to accommodate the pop-up; the displacement probably occurs above regional detachment(s) that project westward beneath the Eagle Plains.