Complex sentence: Authorized as Badlands National Monument on March 4,1929, it was not established until January 25,1939Mission 66 plan, the Ben Reifel Visitor Center was constructed for the monument in 1957-58.
Split into simpler sentences: Authorized as Badlands National Monument on March 4,1929, it was not established until January 25,1939. Under the Mission 66 plan, the Ben Reifel Visitor Center was constructed for the monument in 1957-58.