The Fremont Peak pendant is the largest of many small exposures of “Sur Series” metasedimentary rocks in the northern Gabilan Range which lies along the eastern edge of the central Salinian block, California Coast Ranges. Two periods of folding and three periods of metamorphism were identified in pelitic schist. Early east-west– trending, isoclinal folding accompanied by sillimanite-grade metamorphism formed the dominant structural features. This dynamothermal event predated emplacement of mid-Cretaceous (105 to 110 m.y.) granitic plutons.
Two later periods of thermal metamorphism, during emplacement of granitic plutons, locally reached garnet-cordierite grade with estimated maximum temperature and pressure of 700 to 750 °C and 4.0 kb (±1 kb). Mineral assemblages and calculations suggest that water pressure may have been significantly lower than total pressure in the pelitic schist. A second period of north-south–trending open folding occurred during emplacement of one of the granitic plutons.
The structural and metamorphic sequence in the Fremont Peak pendant is very similar to other sequences in other exposed areas in the central Salinian block.