In 李白's 《蜀道难》, the line 剑阁峥嵘而崔嵬 says Jiange Pass 'towers lofty and steep'. The sense of rising high above the ordinary later carried over to people and to times.
usage
Today mostly figurative: 峥嵘岁月 'momentous years' and 头角峥嵘 'a young person showing outstanding gifts'.
