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Re: [RC] Geology - Barbara McCrary

On the east bay hills, there were several major slippages in the winter of 1997-98. I would say these occurred due to the topsoil being unable to hold onto the subsoil. Whether or not there were cattle on these hills at the time, I don't know. I do know that we had major landslides here at our place in the same winter. We had 71.45" of rain that winter compared to our usual normal average of about 30-32". On one slide, there was a large redwood tree sliding down the hillside on the oozing mud, headed directly for the facilities of the Monterey Bay Salmon and Trout project. We fell the tree so as to stop the sliding, and I think we may have anchored the stump with a cable. On another slide, the whole wall of a bluff slid down, trees, boulders and all, completely obliterating our Powerhouse Grade trail. Later on, we sent a bulldozer operator up the grade to open up the trail. Later yet, the edge of the trail sloughed off down to the creek. You could see where the bulldozer had been, and the tracks just disappeared off the edge of the trail. Now the trail is stable (until we get another rain like that year), but it is narrow and looks down into the creek, about 100 feet below.
Farther up the canyon, another slide let loose on the opposite side of the creek, taking with it many huge trees. There was nothing there...no cows, no logging, no human intervention at all. One has to consider that when there is more rain than the land can absorb, something has to give, and in many cases it is a large mass of topsoil that separates from the subsoil and slides downhill. Saturation and gravity...as simple as that.


Barbara




----- Original Message ----- From: <Sheila_Larsen@xxxxxxx>
To: <ridecamp@xxxxxxxxxxxxx>
Sent: Wednesday, May 02, 2007 9:08 AM
Subject: [RC] Geology




I question the conclusion that all those ripples are caused by the soil and
seismic activity. I understand what you said about the geology of soils
and how they were pushed up, but the slippages that I saw after rain and
the occasional earthquake (where the entire hill slid - quite impressive)
didn't appear to cause that kind of rippling. I can see where the soil
(clay) can get soft and pushed down by hooves though. So interesting
hypothesis but would need more information to convince me : . )
Thanks,
Sheila
916.414.6685


A lovely horse is always an experience.... It is an emotional experience of
the kind that is spoiled by words. ~Beryl Markham



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Replies
[RC] Geology, Sheila_Larsen