Consists of a variety of intrusive rocks including quartz monzonite, monzonite, tonalite, and quartz diorite on Chichagof and Baranof Islands generally west of or along the Peril Strait Fault (Loney and others, 1967; Karl, 1999). Dominant lithologies are white to medium-gray, medium- to coarse-grained, biotite-hornblende tonalite and garnet-muscovite-biotite tonalite, which have a wide range of quartz-to-plagioclase ratios (from approximately 1:4 to 1:1). Plagioclase-rich samples tend to contain hornblende and have a higher color index; quartz-rich samples tend to be hornblende free and leucocratic (Johnson and Karl, 1985). The tonalite contains local zones of fine-grained, rounded, mafic inclusions and occasional pink pegmatitic dikes. Subordinate to the tonalite is medium- to dark-gray-green, medium- to coarse-grained, foliated biotite-hornblende quartz diorite in which hornblende is always more abundant than biotite. Pyroxene-cored hornblende crystals are locally common (Johnson and Karl, 1985). K/Ar ages range from 182 to 143 Ma (Loney and others, 1967; Karl and others, 1988; S.M. Karl, unpub. data) and are commonly significantly discordant; the youngest ages are from samples collected close to the Peril Strait Fault. A single body is also found north of Tenakee Springs, east of the fault on Chichagof Island; it consists of buff to light-gray hornblende-quartz monzonite, hornblende monzonite, and biotite alaskite (Karl, 1999) and yields a K/Ar hornblende age of 147±7 Ma. S.M. Karl (unpub. data) also reports the presence of small areas of Jurassic plutonic rocks in the Tracy Arm area of the Sumdum quadrangle