Archive for the ‘oakland hazards’ Category

Headwater landscaping

26 March 2013

The advantage of living in the highest hills is that there’s no one upstream from you. At the same time, hilltop dwellers may find it easy to forget what it’s like downstream.


This lot sits at the head of a stream valley at the edge of a regional park. The large expanse of impermeable pavement collects rainwater, and the terrace above it discharges more runoff in a large drainpipe. Ordinarily the ground would absorb most of the water and release it gradually, the way that trees are used to. Instead the flow that results here is strong enough to carry away a lot of gravel. Oh well, call in another truckload.

Turn around and track that water and gravel over the property line into the Regional Open Space. With the extra water, the stream is already cutting a deeper channel into its valley. As the years go by, the valley walls will slump into the stream and the trees will fall with them. A big wad of sediment now working its way downstream will clog the habitat below, smothering the bottomland and its ecosystem. Meanwhile the erosion of the stream valley will work its way headward. Eventually, within a lifetime, the spreading collapse will reach the edge of this large lot (and the neighbors’ lots) and whoever owns it will have an expensive problem. This pristine street may disappear from the map, like others before it in the Oakland hills.

I’m not giving a professional opinion here; it’s obvious to common sense. The landscape of the hills is fragile, but expert advice can make living there much more sustainable.

Displacement at the Altenheim

15 January 2013

The Altenheim complex is on top of the northern side of the Sausal Creek valley, just across the freeway from the reservoir near the McKillop slide. There seems to be a little ground displacement here, too.


This view shows the downhill side of the property, on MacArthur Boulevard where it takes a leftward jog north of upper Fruitvale Avenue. The more I explore the stream valleys cutting through the Fan, the more of this I see.

Collecting the Orinda

4 July 2012

Lately I’ve been putting together a rock collection for the Chabot Space & Science Center. The last rock I needed was conglomerate, and I slapped my head and said “Duh! Use the Orinda Formation.” So it came to pass that I was on the Gudde Ridge roadcut, east of the Caldecott Tunnel, admiring that distinctive body of rock. But its exposures were off limits due to the construction.

orinda formation

There were two problems. Finding exposures of the conglomerate was difficult. And once I got close to the rock itself . . .


. . . this magnificent stone turned out to be rotten. You may think of conglomerate as a rugged rock, with all that grit and gravel in it. Indeed it can be. But the young, minimally processed conglomerate of the Orinda Formation doesn’t hold up to sun and weather very well. The pebbles work loose and the matrix turns crumbly in a matter of decades. The stuff in that impressive set of stairstep cuts is actually ready to give way, thudding dull under the hammer and totally useless for my purpose.

In connection with the Caldecott Tunnel work, the Fish Ranch Road offramp looks like it may have some fresh exposures. But it’s fenced off.

orinda formation

In the end, I had to find my conglomerate elsewhere. The fresh stone is beautiful, though, and being able to finish the collection made my day.

orinda formation specimen


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