Mokelumne Peak has the largest body of metamorphic rock in the region, called the Mokelumne Peak roof pendant, extending over an area of 15 square miles (39 km2).

The pendant has concentric zones of different metamorphic rock types around a central core of highly folded and contorted gneiss.

[6] The granite of the batholith surrounding the roof pendant is the granodiorite of Caples Lake.

The granite is medium- to coarse-grained porphyritic hornblende-biotite granodiorite, determined by K-Ar dating to be between 91.7 and 99.6 million years old.

Rocks on the east side of the peak contain arsenopyrite, chalcopyrite, and bornite.