Lecture Notes on Environmental Issues
Sale, Kirkpatrick. 1993. The Green Revolution - The American Environmental Movement 1962-1992. Hill and Wang, New York, 124 pp.
source: http://aggie-horticulture.tamu.edu/syllabi/315/lecture2.html
 
Growth in Membership of Environmental Organizations

Group  before 1962  1970  1980  1991
Audubon Society (1962)  41,000  81,500  400,000  600,000
Izaak Walton League (1966)  52,000  53,600  52,000  50,000
National Wildlife Federation (1966)  271,000  540,000  818,000  5.6 million
Sierra Club (1959)  20,000  113,000  165,000  650,000
Wilderness Society (1962)  27,000  54,000  50,000  350,000
Environmental Defense Fund  150,000
Natural Resources Defense Council  170,000

Total of Group of 10 7,790,000
Source: Sale, Kirkpatrick. 1993. The Green Revolution - The American Environmental Movement 1962-1992. Hill and Wang, New York, 124 pp.