Archive for the ‘the Fan’ Category

Geology of the Biff’s site

22 May 2017

Because I walk through the area regularly, I’ve kept an envious eye on the excavation at the southeast corner of 27th Street and Broadway. Since the building slated for the site doesn’t have a name yet, I’ll call it the Biff’s site after the much-loved but long-departed Biff’s Coffee Shop that once sat there. It’s at the center of the maps below — first the Google terrain map.

Then the historic map. This is from an 1888 map compiled by state surveyor Julius Henkenius, served up by the David Rumsey Map Collection. What I like about it is that it shows the creeks. The main stream is Glen Echo Creek, with the Broadway Branch joining it near the top of the map.

The 27th and Broadway site appears to include the southern half of the Cogswell tract, presumably the remarkable Henry Cogswell whose great monument is a highlight of Mountain View Cemetery.

Anyway, what’s under the ground here? For that, we want the geologic map. This site is at an interesting intersection.

The site is flanked by two lobes of the ancient alluvial fan (Qpaf) that covers central Oakland. The one on the left is Pill Hill — which was known as Academy Hill in the 1880s and the site of Anthony Chabot’s first municipal reservoir — and the lobe on the right is Adams Point Hill. To the south, the ground is mapped as Pleistocene marine terrace deposits (Qmt), and the site itself is mapped as ordinary alluvial sediment.

Knowing all that, it would have been fun to poke around as the excavation proceeded from 24 March . . .

. . . to 1 April . . .

. . . to 19 April . . .

. . . to 7 May, when the digging was complete and the foundation prep was under way.

The chances were that no mammoth skulls or other cool megafossils were present, but you never know. It all looked like well-sorted fine sand from my distant viewpoint, what you’d expect. If this had been a Caltrans project, they might have retained a paleo firm to watch the digging and grab any fossils the dozers turned up. But as of last week the exposure is all over.

Most of the time, science is just an indulgence. But as Oakland enters a downtown building boom, it would be nice if the experts got a chance to document and sample some of these big holes.

Lobe 8 of the Fan: Evergreen Cemetery hill

15 June 2015

Cemeteries occupy some of Oakland’s nicest hillsides. Evergreen Cemetery, unlike the others, has a whole hill to itself. The hill consists entirely of sand, silt and gravel laid down in a large alluvial fan (the Fan) back some time in the Pleistocene. Later, stream erosion cut the Fan into pieces, which I have numbered west to east from 1 to 8. This one’s the smallest and, all things considered, the sweetest.

lobe8-evergreencem

This is the view from 64th Avenue, the hill’s gently sloping side. The NL bus runs past here, too.

Below is the terrain view in google Maps, where I’ve marked it along with lobes 6 and 7.

lobe8-topo

This is the view from across MacArthur Boulevard at 68th Avenue/Church Street. The hill is pretty secluded, with trees screening it on most sides. When you’re there, your eyes are lifted to distant views, which is fitting. The homes on the far side of 68th probably excavated into the edge of the hill when they were built.

lobe8-from-church

When the weather’s right, you can get a good view of it from Outlook hill, for instance from Delmont Avenue:

lobe8-millsmont

or from the overlook at the end of Simson Street. These days the cemetery is doing its part in the drought. Most homeowners are, too.

lobe3-from-simson

The geologic map (as seen in this earlier post) shows a little more Fan alluvium to the north and east of the hill, but it’s topographically subdued.

The Mills College lobe

19 April 2015

The big alluvial fan of old Pleistocene gravel making up Oakland’s most unusual topographic feature—the Fan—is cut by stream erosion into eight lobes, which I’ve numbered from west to east. Lobe 7 is entirely inside the grounds of Mills College, as shown here on the geologic map.

lobe7-geomap

Seminary Creek passes the west side and Lion Creek the east. These streams are responsible for carving the hill away from the rest of the Fan. Of all the bits of the Fan, only this hill and Pill Hill stand isolated from adjoining bedrock. I’m unaccountably fond of both.

Here’s an impression of its topography from Google Maps. The numbers mark the locations of the photos that follow.

lobe7-topo

The hill is densely wooded, for the most part, which limits views of it and views from it. I’ve done what I can, but it’s hard to take in by eye.

I have walked the hills and streets on all sides of this feature, and so far I haven’t found any spot where it stands out in a photo. You have to go there and walk it to get a sense of it. This walk goes clockwise around it. We start where Kapiolani Road is bumped off its straight line by the hill and a footpath takes you up its flank.

lobe7-rise

As I said, most of the hill is wooded, but along the west flank there are spots with a view. The next two photos look from the top of the hill over Seminary Creek’s valley (the creek is culverted here) toward the populated slopes of Maxwell Park hill, lobe 6.

lobe7-to-maxwell1

millshill-over-SemCk

Near the north end of the hill is a footpath down the hill’s western slope to a little-used parking lot along MacArthur Boulevard.

mills-SemCkvalley

From there you can see a fair bit of the hillside.

mills-lobe

You can continue through the woods along Seminary Creek, then take the path past the little graveyard where the Millses, Cyrus and Susan, are buried.

the-millses