Now in its second year, the Ancient Pacific Margin National Mapping (NATMAP) project continues to make progress in elucidating the stratigraphic framework of Yukon-Tanana Terrane of northern British Columbia and Yukon. Updated composite stratigraphic sections for the Finlayson Lake district, Glenlyon, Wolf Lake and Jennings River areas, and from previous studies in the Aishihik Lake area and northern Dawson Range, show that Yukon-Tanana Terrane originated as a dynamic mid- to late Paleozoic (pericratonic) arc system. The evolution of this arc system was punctuated by arc-building events, arc rifting and development of back-arc basins, and episodes of contractional deformation between Late Devonian and early Pennsylvanian. Its development terminated in late Pennsylvanian time with the opening of a marginal basin and the subsequent mid-Permian calc-alkaline volcanism, high-pressure metamorphism and regional deformation of the terrane.