Archive for February, 2013

23rd Avenue valley

26 February 2013

Between the stream valleys occcupied today by 14th Avenue (originally named Commerce Street) and Fruitvale Avenue (Sausal Creek) is a subtle little valley that once had its own little creek. Now 23rd Avenue runs up its former course, diverting the street from the grid so typical of the rest of the neighborhood. The creek is shown on the 1877 map entering the Bay where the Embarcadero Cove Marina sits today. There seems to have been a shellmound a little south of there.

This view is looking up Foothill Boulevard where it crosses the valley. This is at the top of the marine terrace and the foot of the Fan. You can pretty much always tell where the Fan starts by following Foothill. The geologic map shows the valley splitting here with a spur running due north for a few blocks, filled with young alluvium.

23Av-Foothill

This is looking across the valley farther uphill, on E. 17th Street where Garfield Park is. The valley is a bit deeper here, and it continues to deepen as you go uphill.

23Av-E17St

At 23rd and 23rd the creek split, with its northern fork running where Highland Avenue is today. The main fork continued straight, along 23rd Avenue, and petered out by E. 30th Street right next to the Central Reservoir, which is in the Sausal Creek watershed. The stretch where the divide between the two watersheds is most pronounced is occupied by a street named, unsurprisingly, Grande Vista.

This creek is entirely covered today.

Sneak creek peek

22 February 2013

Sausal Creek has escaped culverting in a large part of its course. Between Dimond Park and the freeway, it mostly runs through people’s back yards, but you can spot it looking downstream from MacArthur Boulevard across from Canon Avenue:

sausalsecret1

. . . and farther down, looking upstream from a spot at the intersection of Dimond Avenue and Montana Street.

sausalsecret2

It’s culverted from here all the way down to the end of Hickory Street, directly below the miserable house on McKillop Street. Maybe it’s safer to say that the creek is covered, because even this open stretch has walls hemming it in.

Smilodon californicus

15 February 2013

If you’re at UC Berkeley with a little time to spare, go visit the Valley Life Sciences building and say hi to the sabertooth cat fossil there.

smilodon

Smilodon californicus is our official state fossil. It got the honor from its abundance in the tar pits of Rancho La Brea down in Los Angeles. It turns out that they were suckers, walking into the tar to feed on animals already stuck there, then getting trapped themselves. They and the extinct dire wolf are the two most common species in the tar pits.

Presumably they lived in Oakland, but I don’t see any reference to local Smilodon fossils. One of the things on my to-do list is to visit the paleo people at UC Berkeley and learn more.

Dimond valley

6 February 2013

Sausal Creek is responsible for digging a floodplain that is rather wide just upstream from I-580. Here’s the view across it from Montana Street at MacArthur.

uprdimond1

The squat tower just to the left of the speed limit sign is at the foot of Lincoln Avenue, and it’s at the same elevation as where I’m standing. That’s how wide the valley is. Here’s another view looking right down MacArthur.

uprdimond2

The first cross street is Canon Avenue, the next one is Dimond Avenue leading up to the park, and beyond is the Fruitvale Avenue crossing. Here’s how the geology is mapped.

uprdimondmap

You can see that the stream valley is wide because three streams coalesce here at the edge of the Piedmont bedrock block. Restricted upstream, they enter the big alluvial fan (Qpaf) and have room to move and easy material to erode. It is curious that Sausal Creek hugs the west side of the valley; I suspect that tectonic movements may account for that, but only a decade or so of careful satellite altitude monitoring can answer my suspicion.


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