Over time they were slowly changed by pressure and heat into the complex variety of metamorphic rocks present today: schist, quartzite, gneiss, and several outcrops of white marble. During the last ice age small glaciers sculpted the Siskiyou basins that now contain lakes and meadows.
Metamorphic rocks evolved over time through a series of transformations caused by external forces like pressure and heat into the varied types present today: schist, quartzite, gneiss, and white marble. The last ice age also reshaped the Siskiyou basins, now housing lakes and meadows.