Archive for the ‘sausal creek watershed’ Category

Fruit Vale

27 June 2013

The valley of Sausal Creek below Dimond Canyon made a natural site for orchards: a nice flat floodplain with decent soil and a permanent stream off on the western side. Also, the valley is straight to a degree that strikes me as unusual, which is handy for laying out blocks of land. It may or may not have been filled with oaks—I have a copy of an old print titled “Oaks of Oakland” that purports to be from this area. In any case it has a classic shape with a flat floor and steep sides formed by the Oakland alluvial fan (the Fan). I’ve shown the high, landslide-prone western side before; here’s the eastern side. This is the view from the Fruitvale freeway exit looking up Harold Street, where the valley wall is pretty dramatic.

fruit-vale-harold

Farther down, the valley wall fades away well before you get to Foothill Boulevard, which everywhere marks the edge of the Fan. Here at Fruitvale Boulevard and Bona Street, the valley wall is already lower and more subdued.

fruit-vale-bona

It looks like I’ll name this lobe of the Fan the Patten lobe. The valley of Peralta Creek is just over the hill. It’s interesting to speculate why the Peraltas put their rancho buildings there rather than here.

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.

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.

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.

altenheim-slump

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.

Sandstone concretion, Joaquin Miller Park

11 January 2012

This odd tumorous-looking thing, on a sandstone boulder in the Oakland Conglomerate in Joaquin Miller Park, is a concretion.

concretion

I’ve documented concretions in Oakland before, in rocks of the Great Valley Sequence and in the nameless unit of Eocene mudstone above Shephard Canyon. This concretion is unlike the other two in (I assume) not having a siliceous matrix like the first and not being finely layered like the second. I assume that this is a typical featureless ball of extra-strong mineralization that formed slightly before the rest of the rock lithified. (And on KQED Quest Science Blogs this week, I talk about other concretions in the Bay area and California.)

By the way, I visited the lower end of Joaquin Miller Park the other day, below the Woodminster area where the Miller cottage is, and finally saw my sign about the rocks of the park. I hope that people have gotten some benefit from it.

Franciscan rocks of Dimond Canyon

13 May 2010

The last piece of bedrock I want to show from the Sausal Creek watershed is the Franciscan Complex. It crops out on the west side of the Hayward fault, unlike all the other ones I’ve been showing, but it’s roughly the same age as the Shephard Creek–Redwood Canyon package, 80 to 70 million years old. This is a sandstone outcrop just uphill from the Zion Lutheran School on Park Boulevard. It’s part of the Novato Quarry terrane.

franciscan outcrop

The sandstone is hard and gray, composed of fairly well sorted sand. The other week a geologist chided me (and the rest of my field-trip group) for our habit of calling this graywacke. It’s not graywacke unless it has at least 10 percent clay, he said. So OK, this is sandstone. And the bluish color is reflected skylight; sorry about that too.

sandstone

As you come in the school driveway, you’re greeted (if you’re paying attention) by this fine outcrop of mélange.

melange

I didn’t linger the day I took these photos because the yard was full of kids and two patrol cars were sitting there. I have a plan for any time that police want to check me out: I’ll start talking all about geology and showing them rocks and stuff, so they’ll know I’m a harmless nut. I tried it once, up in the Sierra, but it was a time of terrible wildfires and the sheriff just went back to his car and waited until I moved on.

Serpentinite of Visionary ridge, Joaquin Miller Park

6 May 2010

The ridge behind Woodminster Theater, in Joaquin Miller Park, is mapped as serpentinite. You start to notice this around the Moses pyramid, but as you explore you’ll find a lot more of it plus various associated metamorphic rocks.

joaquin miller serpentinite

For instance, on the Siwalik Loop Trail I spotted a fine chunk of actinolite schist, detailed below.

actinolite

The ridge doesn’t have a name on the map, so I’ll give it one. It has the Moses pyramid, the Elizabeth Barrett Browning monument, the fireplace that Joaquin Miller built for his own cremation, and Lookout Point where Miller loved to contemplate Oakland and the bay. So by my decree, this is Visionary ridge.

At Lookout Point, the large boulders surrounding the viewing patio caught my eye. High-grade blocks!

blueschist

A closer look showed me the garnet-muscovite-glaucophane association that marks blueschist. There was also some green (chromian) mica. Bring your magnifier, not your hammer, if you come this way.

blueschist


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