The Central Metamorphic Belt and Trinity terrane of the Klamath Mountains and the Feather River terrane of the northern Sierra Nevada share strong similarities in their protolith types, metamorphic parageneses, structures, ages of formation and metamorphism, and relations with surrounding units. These terranes consist of ductilely deformed ultramafic to mafic plutonic and volcanic rocks and minor oceanic sedimentary rocks interpreted as oceanic lithosphere. Ultramafic rocks in the Trinity terrane and the Feather River terrane were hydrated and metasomatized under lower amphibolite-facies conditions. Mafic and sedimentary rocks in the Central Metamorphic Belt and the Feather River terrane contain upper greenschist to amphibolite-facies parageneses formed during Devonian time. Phase assemblages and mineral chemistries indicate peak P-T conditions of 500° to 650 ± 50°C and 500 ± 300 MPa for both terranes. The similarities imply that the Klamath Mountains and Sierra Nevada share a common early to middle Paleozoic history. The Trinity terrane/Central Metamorphic Belt represents an arc basement/subduction zone couple; the Feather River terrane may also represent such a couple.