in the southern rocky mountains, near present-day colorado, these ancestral rocks were disturbed by mountain building about 300 mya, during the pennsylvanian. this mountain building produced the ancestral rocky mountains. they consisted largely of precambrian metamorphic rock forced upward through layers of the limestone. the limestone had been laid down in a shallow sea. the mountains eroded throughout the late paleozoic and early mesozoic, leaving extensive deposits of sedimentary rock.