Complex sentence: The 1979 Imperial Valley earthquake occurred at 16:16 Pacific Standard Time (23:16 UTC) on October 15 just south of the United States-Mexico border and impacted the Imperial Valley in southeastern Southern California and the Mexicali Valley in northern Baja California.
Split into simpler sentences: The 1979 Imperial Valley earthquake occurred at 16:16 Pacific Standard Time (23:16 UTC) on October 15 just south of the United States-Mexico border. It affected the Imperial Valley in southeastern Southern California and the Mexicali Valley in northern Baja California.