Active epoch: Early Public Concern (1870 - 1920), Initial Organized Efforts (1920 - 1937)
Active epoch: Initial Organized Efforts (1920 - 1937)
Active epoch: Period of Federal Support (1966 - present)
Active epoch: Exemplars & Testing of Legislation (1937 - 1966), Period of Federal Support (1966 - present)
Active epoch: Initial Organized Efforts (1920 - 1937)
Active epoch: Early Public Concern (1870 - 1920)
Active epoch: Exemplars & Testing of Legislation (1937 - 1966), Period of Federal Support (1966 - present)
Active epoch: Early Public Concern (1870 - 1920)
Active epoch: Initial Organized Efforts (1920 - 1937), Exemplars & Testing of Legislation (1937 - 1966)
Active epoch: Period of Federal Support (1966 - present)
Active epoch: Early Public Concern (1870 - 1920)
Active epoch: Initial Organized Efforts (1920 - 1937), Exemplars & Testing of Legislation (1937 - 1966)
Active epoch: Period of Federal Support (1966 - present)
Active epoch: Period of Federal Support (1966 - present)
Active epoch: First Interests (pre-1870)
Active epoch: Initial Organized Efforts (1920 - 1937), Exemplars & Testing of Legislation (1937 - 1966)
Active epoch: Exemplars & Testing of Legislation (1937 - 1966)
Active epoch: First Interests (pre-1870)
Active epoch: Exemplars & Testing of Legislation (1937 - 1966), Period of Federal Support (1966 - present)
Active epoch: Exemplars & Testing of Legislation (1937 - 1966)
Active epoch: Early Public Concern (1870 - 1920), Initial Organized Efforts (1920 - 1937)
Active epoch: Period of Federal Support (1966 - present)
Active epoch: Exemplars & Testing of Legislation (1937 - 1966)
Active epoch: Period of Federal Support (1966 - present)
Active epoch: Initial Organized Efforts (1920 - 1937)
Active epoch: Period of Federal Support (1966 - present)
Active epoch: Initial Organized Efforts (1920 - 1937)
Active epoch: Period of Federal Support (1966 - present)
Active epoch: Period of Federal Support (1966 - present)
Active epoch: Initial Organized Efforts (1920 - 1937)
