Archive for November, 2009

Driveway of delight

29 November 2009

On a walk in North Oakland in connection with my hobby, I was delighted to see another example of a homemade decorative driveway. This is just the beginning of it:

rock driveway

Whoever built it had access to big chunks of waste glass as well as a variety of rocks from near and far. One of those, the green one in the lower right, is a fine specimen of actinolite schist:

actinolite

To my knowledge, you won’t find such a thing in Oakland. I got my first hand specimen of actinolite from that rock shop on 101 next to Squaw Rock on the Russian River, south of Hopland. I asked the owner, as I often do, “What do you have that’s local?” and he handed me that one. The boulder in this driveway looks just the same.

Oakland from the air

22 November 2009

airship

I have got to save up the money to ride the Eureka, our local airship, to survey Oakland from above. Good as Google Earth is, or a ride in a small plane, there is nothing like the leisurely, quiet flight of a lighter-than-air craft for viewing and photographing the ground. (Click the photo for a larger version.)

San Leandro Creek (2)

16 November 2009

San Leandro Creek is Oakland’s largest watercourse. Before Anthony Chabot dammed its upper reaches and the Bay shore was filled in, the creek was navigable up to East 14th Street. Where you enter the M. L. King Regional Shoreline at Hegenberger Road, San Leandro Creek looks quite capacious.

san leandro creek

Today the creek no longer has a lazy, sinuous course but instead runs down a straight ditch to its mouth near the Coliseum. The water looks wholesome, there’s wildlife all around, and the fishing seems to be good. Today’s paper showed men pulling sardines out of the bay here.

san leandro creek

An elaborate observation tower offers a view of San Leandro Bay, an unsung body of water between Alameda Island, Bay Farm Island and the mainland. My visit was near high tide; the map shows it as almost all mudflats.

san leandro bay

The spear of grassy marshland is Arrowhead Marsh. One story has it that the marsh was created in 1879 when Chabot’s dam construction, accomplished with hydraulic hoses, washed an enormous quantity of sediment down to the Bay. If so, that would be just another item in the long list of damages done to California during early statehood. But just as likely is that it was always there, along with 2000 more acres of marsh stretching across today’s airport and in a wide fringe around San Leandro Bay.

Here’s a view of the creek’s course across the East Oakland flats.

Treasure!

12 November 2009

excavation

Where the subsurface is inaccessible, you learn to prize the opportunities to sample it. A house on the crest of Montgomery ridge is upgrading its foundation, and the contractor has helpfully kept the tailings in this handy bin. It’s mostly sand and mud, but there’s a good deal of the Franciscan sandstone in it as well, plus hunks of the lovely red chert that seems to be part of the youngest detrital beds all over this hill. I restricted myself to collecting just one chert piece to add to the pile in the front yard.

I keep thinking that a concerted effort by enough Oakland citizens could help ensure that these ad-hoc trenching studies are properly exploited for their scientific value.

Rocks of Leona Quarry Con’d.

7 November 2009

Along the entryway to the Leona Quarry development is a tumble of big decorative boulders, ready for deployment in the landscaping. When I drove by I made a mental note to check them out. I assumed they were chunks from the quarry itself. No such luck; they’re exotic blocks full of shell fossils, which are unheard of in Oakland. This is a view of the shell faces.

leona fossils

This boulder is almost what geologists call a shell hash or coquina, but the shells are mostly intact. I might call it a shell marl instead, but the default name would be fossiliferous limestone. I have no idea where it’s from—somewhere over the hills, or maybe in the Santa Cruz Mountains, but not Oakland.

leona fossils

Here’s a closeup of another boulder showing a cross section of the shells.

leona fossils

This boulder is closer to a shell hash; it’s mixed with sedimentary rock clasts. A few of the darker clasts have released iron, presumably from sulfide minerals. This formed in a very active coastal setting.

leona fossils

It’s a fascinating set of boulders, but an arbitrary one. It also includes big hunks of shale that have disintegrated in the sun and rain here. Who picked them, and why?


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