1872: Yellowstone, first national park, established.
1892: John Muir founds Sierra Club.
1898: Pollution of navigable waters banned by Rivers and Harbors Act.
1905: National Audobon Society founded.
1908: Grand Canyon set aside as national monument, under Antiquities Act of 1906.
1920: Mining on federal lands regulated by Mineral Leasing Act.
1930: Chlorofluorocarbons (CFCs) declared safe because nontoxic, noncombustible.
1936: National Wildlife Federation formed.
1948: Federal Water Pollution Control Law passed.
1956: Echo Park Dam project dropped in Colorado, a wilderness protection victory.
1962: Rachel Carson's `Silent Spring' published, exposing dangers of pesticides.
1963: First Clean Air Act provides funds for air-pollution control.
1966: During a four-day atmospheric inversion, some 80 people die in New York City.
1969: Oil spill in Santa Barbara alerts public to pollution issues.
1970: Earth Day celebrated for first time on April 22.
National Environmental Protection Policy Act passed; requires environmental impact statements.
1972: Clean Water Act passes; to restore polluted waters and eliminate discharges of pollutants.
First United Nations Conference on the Human Environment, in Stockholm.
Oregon passes nation's first bottle-recycling law.
1973: US passes Endangered Species Act after 80 nations sign ban on trade in endangered species.
1975: Atlantic salmon return to the Connecticut River after a 100-year absence.
1976: National Academy of Sciences reports that CFC gases from spray cans damage the ozone layer.
1981: Quebec says 60 percent of its sulphur dioxide pollution is from US industry.
1983: Reagan's Interior Secretary James Watts resigns under fire from environmentalists.
1987: 24 nations pledge to halve CFCs by 1999; later amendment requires phasing out by 1999.
1988: Dumping of wastes in oceans outlawed by international Ocean Dumping Ban agreement.
1989: Timber sales in Alaska's Tongass National Forest halted by Congress.
1990: Clean Air Act amended to include emissions of sulphur dioxide and nitrogen.
1992: Bush attends Earth Summit in Brazil.