Complex sentence: This airport should not be confused with the W.K. Kellogg Airport in Pomona, California, which operated from 1928 to 1932 and was then the largest privately owned airport in the country.
Split into simpler sentences: This airport should not be confused with the W.K. Kellogg Airport in Pomona, California. That operated from 1928 to 1932, and was then the largest privately owned airport in the country.