Periods

20th Century ( 1901 a.d. to 2000 a.d. )	Sites
Early 20th Century ( 1901 a.d. to 1932 a.d. ) Mid 20th Century ( 1933 a.d. to 1966 a.d. ) Late 20th Century ( 1967 a.d. to 2000 a.d. )