Comments for Oakland Geology

Comment on Rocks of Leona Quarry Con’d. by Andrew

Andrew — Mon, 09 Nov 2009 18:48:03 +0000

That shows how parochial I am. I haven’t gotten around to visiting the Briones Formation. Looks like it will be fun.

Comment on Rocks of Leona Quarry Con’d. by P J Evans

P J Evans — Mon, 09 Nov 2009 05:08:15 +0000

I found a small rock like that along Arroyo del Valle, south of Livermore, in the 1960s. (Don’t know where it is now; I’ve moved enough times that it probably got left behind somewhere.)
It had some recognizable turret shell bits, including one lengthwise cross-section, but was mostly just shell hash.

Comment on Rocks of Leona Quarry Con’d. by Jacob Lee Fink

Jacob Lee Fink — Mon, 09 Nov 2009 04:31:21 +0000

Those rocks with the shells in the gray sandstone/siltstone are locally known as Briones Formation. Indeed shallow marine environment. They can be seen all around peaks about the East Bay. I have seen similar rocks at Mission Peak in Fremont and around the Norris Canyon area between San Ramon and Castro Valley.

Comment on Rocks of Leona Quarry Con’d. by Andrew

Andrew — Mon, 09 Nov 2009 01:55:07 +0000

Las Trampas–that would be over the hills. It’s been on my list of places to visit for years.

But these rocks aren’t the kind you would get from a landscaping company, I don’t think. They struck me as the kind of rocks a big homebuilding contractor might have lying around from another project, like one in Tracy or, as you suggest, in the San Ramon Valley.

Comment on Rocks of Leona Quarry Con’d. by Jef Poskanzer

Jef Poskanzer — Sun, 08 Nov 2009 20:04:26 +0000

Cool. Las Trampas has a bunch of these, are there any quarries near there?

Comment on The Rocks of Leona Quarry by Andrew

Andrew — Sun, 08 Nov 2009 00:29:35 +0000

I've been doing some reading about the Coast Range Ophiolite, of which the Leona Quarry rocks are a part. The most recent work I've seen considers this rock not a lava, but a highly compressed and altered tuff, that is, the ash and rubble erupted from volcanoes. So the little flat features in the last photo would be the remnants of lapilli: pebble-size particles, like bits of pumice or lava, that are now almost erased. It's thought to be about 150 million years old, unlike the far younger volcanic rocks of Sibley volcano.

Comment on A glimpse below by Naomi Schiff

Naomi Schiff — Fri, 23 Oct 2009 00:26:41 +0000

Interesting aspects were that a) originally the Diocese wanted to build on the Kaiser Auditorium parking lot at 12th Street, which is on 100% fill, and atop the old waterway between bay and what is now Lake Merritt; b) that they had to pump water out of the construction hole at this site for so many months, reminding me of construction of Moscone Center; c) that the prominent corner of Grand/Harrison is treated dismissively, like an incidental back door, d) that it re-uses a historic Catholic site, the original location of College of the Holy Names.

The sanctuary itself is impressive but the concrete podium is dreary. (Since it is also a mausoleum maybe this is appropriate.) To me it ignores the original topography in an unfortunate way, separating itself from the sidewalk pedestrian and from the historic grade level. You can get a sense of how the area originally consisted of streams running into marshes, with wide flat areas. The slope up doesn’t really start until 27th Street.

Comment on A glimpse below by Erik

Erik — Wed, 21 Oct 2009 17:40:09 +0000

I think it’s safe to assume that the designer was aware of the earthquake risk.

Comment on A glimpse below by farmlady

farmlady — Wed, 21 Oct 2009 16:28:03 +0000

Very interesting. I saw the completed Cathedral when I visited my son a few months back. It amazing!
I would hope that it holds together in the coming “big one”. Future geologist may find a small layer of petrified glass between the layers of golden sand and aboriginal sediment.
I hope Jesus’ image in the glass protects all those parishioners that believed building a structure like this in an earthquake prone area was a wise idea.

Comment on City Hall and the Loma Prieta Quake by Garry Hayes

Garry Hayes — Mon, 12 Oct 2009 03:05:18 +0000

Now, we just wait and see if the engineers were right!