I'm curious where you ran across the term "Keystone Park entrance".  I have never heard it called or even referred to as that term, although I keep seeing it on these boards. It was, in fact, the Memorial Entrance and more commonly referred to as the old Ceremonial Gate or Entrance.  The facade was built as a retaining wall for the hill behind.  As of 1997, it is WIMSA, the Women in Military Service to America Memorial.  What was originally just a retaining wall was dug out behind and is now an actual building containing exhibits etc.    Women in Military Service to America Memorial