The Central Belt of the northern Sierra Nevada at Oroville Lake, California, includes large outcrops of Permian limestone as clasts surrounded by siliceous diamictite. Limestone ranges from pebbles to megaboulders as much as 100 m in size, and five clasts contain Wolf-campian to Leonardian corals and fusulinids. The diamictite which encloses limestone clasts has a pebbly mud texture and a chaotic fabric. Paleozoic megafossils occur in the mud matrix of the diamictite, and mixing of limestone clasts and diamictite was a Permian event. The diamictite and enclosed limestone megaboulders, collectively termed a “megamictite,” probably represent a base-of-slope sedimentary deposit. Limestone boulders and megaboulders are tabular stratigraphic fragments which detached from lithified carbonate escarpments and moved downslope by sliding along their flat surfaces. Lithologies of limestone clasts indicate derivation from a shallow carbonate platform. Corals and fusulinids within limestone clasts include endemic taxa found in the McCloud Limestone of the Eastern Klamath Mountains, and they represent a Permian biogeographic province distinct from those of western terranes of the Klamath Mountains and the North American craton. A large carbonate platform in the eastern Klamath area is proposed as the source of limestone clasts in the Central Belt at Oroville Lake.