Complex sentence: El-Amra was the first site where this culture group was found unmingled with the later Gerzean culture group; however, this period is better attested at the Naqada site, thus it is also referred to as the Naqada I culture.
Split into simpler sentences: El-Amra was the first site where this culture group was found unmingled with the later Gerzean culture group. However, this period is better attested at the Naqada site, and so is also referred to as the Naqada I culture.