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That diversity is due to the subtropical latitude, altitudinal variation in the basin and range topography, and a confluence of floras of northern Rocky Mountain with the southern Mexican Sierra Occidental.  Geologists think that 40 million years ago the area was a high flat plain. About 12 mya basin and range topography developed due to stretching (up to 80 per cent) of the land towards the west by the northwest movement along the San Andreas fault in California. Erosion since that time has resulted in filling of the basins around Tucson and Sonoita of over 5,000 feet of sediment. From fossils found in the San Pedro River Valley to the east we know that Wooly Mammoths, Camels, Rhinos, Bears and large cats roamed the area in the last few million years. The continuous evolution and development of the flora and fauna continues in the multitude of habitats of the region. Bob will try to elucidate a small number of known interrelationships as well asgive a hint of the flora of the region.

Bob has been a naturalist since 1962. His career includes teaching biology in the California public schools ( Junior High, High School, Junior College), biologist/teacher at Point Reyes Bird Observatory (1968-1979), naturalist for Marin County Open Space District (1982-1997) (where he gave over 2,000 free walks to the public), and he has lead innumerable outings to California, Arizona, Texas, Mexico, Costa Rica, and Trinidad and Tobago. He has self published two photographic butterfly books: Common Butterflies of California (1997) and Butterflies of Arizona (2001).