Composed of columnar-jointed andesite and basalt lavas that locally contain interbedded tuff, breccia, and agglomerate, this unit is exposed in two general areas, the largest of which is a belt in west-central Alaska. In the Takhakhdona Hills of the Melozitna quadrangle, dark-green to black vesicular basalt flows formerly mapped by Patton and others (1978) in their unit TKv are now known to be of Tertiary age. Isolated exposures include the Roundabout Mountain volcanic field in the Kateel River quadrangle and olivine basalt flows on the eastern part of the boundary between the Bettles and Tanana quadrangles. The second area of exposure is in the Talkeetna Mountains quadrangle, where there are outcrops of predominantly reddish-brown-weathering, aphanitic to porphyritic basaltic andesite and basalt lavas, often columnar-jointed, and including lesser tuff, and local cinder deposits (Csejtey, 1974, Anderson, 1969, Oswald, 2006). Individual flows and tuff beds are tens of meters thick; as a whole, unit may be several hundred meters thick. A small area of basalt flows is also mapped in the western Lime Hills quadrangle (Wilson and others, 1998). K/Ar isotopic cooling ages range from 65.2±3.9 to 38.6±2.4 Ma