2. 1845: Naturalist Henry Thoreau spends two years in Walden woods observing and recording rainfall, temperature and plant growth. Thoreau published book and promoted the protection of wilderness.
3. 1891: Congress establishes Yellowstone as first national park; simultaneously passes bill that legalizes mining in public areas for a fee.
4. 1889: John Muir (with the help of magazine editor Robert Johnson) introduced bill to Congress to make Yosemite a national park.
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6. 1892: The Sierra Club is created and co founded by John Muir, who becomes its first president. It is currently the largest grassroots environmental organization of the U.S.
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13. 1972: DDT, the toxic synthetic pesticide, becomes banned in the U.S.
