Complex sentence: It was opened to the public on June 7th, 1982 and was listed in the National Register of Historic Places on November 7,1991 and declared a National Historic Landmark on March 27,2006.
Split into simpler sentences: It was opened to the public on June 7th, 1982. The site was listed in the National Register of Historic Places on November 7,1991 and declared a National Historic Landmark on March 27,2006.