Abstract Mafic schists in California carry the typical blueschist facies assemblage of glaucophane—crossite + lawsonite 4 sphene + chlorite ± aragonite or calcite ± pumpellyite. Albite, epidote and actinolite are not common in “in situ” metabasalts. In contrast, typical Sanbagawa schists contain crossite or actinolite + albite + epidote + chlorite ± calcite; the highest-grade rocks generally contain garnet and blue—green hornblende, lower grade rocks may contain pumpellyite and/or stilpnomelane, rarely lawsonite. Franciscan metaclastic rocks show three principle assemblages, all of which contain the phases quartz 4 white mica + chlorite + sphene ±lawsonite ± stilpnomelane: albite 4 calcite, albite 4 aragonite; and jadeitic pyroxene ± aragonite ± glaucophane. Quartzose Sanbagawa metaclastic rocks represent the albite ± calcite type compatibilities; lawsonite, aragonite and jadeitic pyroxene are either absent or are very rare. Many Franciscan siliceous metasediments contain, in addition to quartz, the phases riebeckite, stilpnomelane and/or spessartine. In contrast, many Sanbagawa siliceous schists carry abundant piemontite ± magnesioriebeckite in addition to spessartine. Correlation of the above mineral assemblages with experimental data suggests that blueschist-facies metamorphism took place in the Franciscan terrane at high fluid pressures, and involved temperatures of 200–300°C and lithostatic pressures of 6.5–8 kbar. Apparently Sanbagawa metamorphism reflected physical conditions transitional between the blueschist, greenschist and albite—epidote—amphibolite facies, approximating 250–400°C at 5–7 kbar lithostatic pressure.