Monday, April 27, 2009

Scenes from the Mt. SAC Conference, April 17-19

Many thanks to Wendy Van Norden! Some sights from the Mt. San Antonio Canyon field trip at the recent conference of the Far West Section at Mt. SAC in Walnut, California.

I wasn't able to attend, but I recognize a few of the features, and hope Wendy or others will correct any misinterpretations in the comments. The top photo is the Hogback, a rather large rockslide in the upper canyon. When I was growing up, this was the hill that challenged my 1965 VW Bug, and I was always intensely curious about why the road went so steep over the top, when it made more sense to go around it. The answer is in the second photo: the road used to do that, but was wiped out in the catastrophic floods of 1969. San Antonio Canyon was always a difficult place to try living in or developing. It seems the only places flat enough for buildings are on the top of landslides, or on sediments backed up behind landslides. These are steep mountains!

The remaining photos show faults and dikes exposed in the upper canyon. The bottom photo is a great exercise in crosscutting relationships! I see at least two dikes and two faults. Which came first and what was last?? (click on the images for a slightly larger view)

Thanks again, Wendy.

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