File:Moro Rock exfoliation dome (Giant Forest Granodiorite, mid-Cretaceous, 97-102 Ma; Sequoia National Park, California, USA) 3 (16799537885).jpg

Summit of Moro Rock exfoliation dome

Moro Rock is a large exfoliation dome in the Sierra Nevada Mountains of eastern California, USA. It is accessible by road and hiking trail in the western part of Sequoia National Park, a little east of Generals Highway (Rt. 198).

Exfoliation domes are common in the Sierra Nevada Mountains. They form by large-scale spheroidal weathering of granites and granitoids of the Sierra Nevada Batholith. The batholith represents a Late Jurassic to Late Cretaceous-aged mass of cooled magma chambers originally beneath a chain of subduction zone stratovolcanoes.

Pressure release from erosional unroofing of the batholith resulted in the rocks having curved sheeting joints. Spheroidal weathering followed, akin to peeling the layers from an onion (“exfoliation”). The end result is a rounded mountain top - an exfoliation dome.

Moro Rock is the type locality of the Cretaceous-aged Giant Forest Granodiorite, one of numerous specific igneous intrusions in the Sierra Nevada Batholith. Granodiorite is dominated by quartz and sodic plagioclase feldspar and some potassium feldspar. The Giant Forest Pluton is also rich in hornblende amphibole (= black crystals) and relatively rich in small, ~honey-colored crystals of titanite (a.k.a. sphene - CaTiSiO5).