Complex sentence: Most South Africans in the United States are currently settled in San Diego, CA: approximately 20,000 people, although elsewhere in the western United States and in the Pacific Northwest lacks significant numbers of South African Americans.
Split into simpler sentences: Most South Africans in the United States are currently settled in San Diego, CA: approximately 20,000 people. In the western United States and in the Pacific Northwest, there are not significant numbers of South African Americans.