3 November 2007 Talk On Brodiaea santarosae And Geology Of The Santa Rosa Plateau

The following links give the viewgraphs, animations, etc. used for the Docent Class Talk:

• Brodiaea santarosae

  • Pictures

  • Pictorial Key To The Species Of Brodiaea In Southern California

  • Geographic Distribution

• 5 minute oral overview of geology of the Santa Rosa Plateau: "Three Rocks, Three Stories":
  • Woodson Mountain Granodiorite: ~100 million years old, forms white boulders on the surface, rock cooled slowly in underground magma chamber for the volcanoes formerly present in southern California similar to Mt. St. Helens.

  • Bedford Canyon Formation: ~100 million years old, former sediments deposited on sea floor from erosion of edge of North America continent, metamorphosed by being next to the underground magma chamber. Erodes easily, and so is almost never seen on the surface. Rocks show the deformed sedimentary layers. (Actually not a single rock type; consists of altered shale, conglomerate, limestone, etc.)

  • Santa Rosa Basalt: ~10 million years old, deposited by a spreading center on the flat land that existed in southern California then. Found on flat-topped mesas. The dark brown / blackish rocks often have frozen air bubbles.

• Viewgraphs on Santa Rosa Basalt (only first three viewgraphs, up to geo_2.html)

• Pictures Showing Geology Throughout the Santa Rosa Plateau

• Examination of samples of the actual rocks

• Geology From Google Earth Throughout the Santa Rosa Plateau (the pictures have all had their contrast adjusted quite a bit in order to show the Woodson Mountain Granodiorite boulders.)

• Geologic Map of Public Area of Santa Rosa Plateau (adapted from Turner and Loera 2003. My map does not include the very small mapped areas of Gabbro, Santiago Peak Volcanics, and Tertiary arkosic sand and gravel)

• Geologic Animations from The Educational Multimedia Visualization Center of the Department of Earth Science, U.C.S.B., Tanya Atwater, Director.

  The ones I showed, in order, are:

  1. Pacific Hemisphere Plate, 80Ma to Present
  2. Mesozoic Subduction
  3. Southern California, Origin and Dispersal of the Poway Conglomerate
  4. Plate Tectonic History of Southern California, 20 Ma to Present (stable North America held fixed)
  5. Southern California, 20 Ma to Present
  6. Southern California Paleomagnetic Vectors
  7. Miocene: Rifting and rotation, volcanism, crustal upwelling and deposition in marine basins
  8. Plio-Pleistocene Oblique Shortening against the San Andreas fault
  9. N.E. Pacific and W. North America Plate History, 38 Ma to Present.

Bonus link:

The 2007 Fallbrook Fire: A Fire In A Suburban Rural Landscape

Go to:

• Field Guide to the Santa Rosa Plateau
• Hiking the Santa Rosa Plateau

Copyright © 2007 by Tom Chester.
Permission is freely granted to reproduce any or all of this page as long as credit is given to me at this source:
http://tchester.org/srp/geology/2007_talk.html
Comments and feedback: Tom Chester
Updated 2 November 2007.