Complex sentence: They are properly referred to as the world's only "conoidal" the domes covers 15,000 square feet of display area and were constructed in stages from 1959 tothe late 1980's when the area was filled in due to budget cuts.
Split into simpler sentences: They are properly referred to as the world's only "conoidal" domes. They cover 15,000 square feet of display area and were constructed in stages from 1959 to the late 1980's when the area was filled in due to budget cuts.