Archive for the ‘oakland soil’ Category

The I-980 swath

1 March 2013


Interstate 980 is a huge convenience for drivers. I appreciate it every time I drive around town. But its construction was a major injury to Oakland’s neighborhood fabric, splitting West Oakland from downtown harshly and irrevocably. Every time I walk over 980, as here on the 14th Street overcrossing, I ask, Did they really need to hack out all this space for the freeway? Farther north, where the road becomes route 24, it’s narrower and they left a fringe of homes on Martin Luther King bordering the highway. But on 980, the excavation took out a full city block between Castro and Brush streets.

Maybe the difference was the sand. I-980 is built in the Merritt Sand, which underlies downtown and West Oakland up as far as Grand Avenue. The ancient dune sands probably can’t sustain a steep slope on the sides of the freeway. And the builders had to dig deep to make room for the overcrossings—most of the other freeways are not below grade. A narrower roadway, with tall vertical soundwalls on either side (like the new part of the Nimitz farther west in Bay mud), would not be as safe during earthquake shaking, and without room for the vegetation it would be a dreary place indeed. Bad as it is, it could have been worse.

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.

Longridge loess

21 August 2012

I was walking up Longridge Road and spied an excavation, where a homeowner was replacing some water lines and renewing a driveway. Naturally, I sidled over and took the rare chance to look beneath the skin of Oakland’s Pleistocene fan. The material was massive—unbedded—and clean. I pried off this little piece . . .


. . . and nibbled on it. It was firm, but crumbled like Necco wafers and turned creamy on the tongue with just a hint of grit. Not sticky or chewy with clay. Not indurated like hardpan. No sand or pebbles to be seen. The more I thought about it, the more peculiar this sediment seemed, until I had a wild surmise.

Alluvial sediment is never very well sorted, because it’s carried short distances and laid down by streams. Longridge Road is, as the name suggests, a ridge road running up the crest of a ridge between parallel stream valleys along Trestle Glen and Mandana roads. The crest of a ridge should not be made of this fine silt. But it’s downwind from downtown, which is Pleistocene sand dunes (the Merritt Sand), cousin to the dunes of San Francisco. Dune sand is very fine sand, and the fraction that blows away from the sand is finer still. So my wild surmise is that the fan, at least this part of it, is dusted with a layer of windblown glacial silt—i.e., loess. It’s remarkable stuff, and something I never expected to see in Oakland.


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