Oakland Geology

This hills-and-paths walk is number 20, “Broadway and Oak Glen Park,” in Charles Fleming’s Secret Stairs East Bay. This is not a bedrock walk, like the previous ones I’ve featured, but a landform walk. Let’s start this time with the topography.

This walk starts in the bayside flats, crosses two hills and two streams, and returns from the side of a third hill. The first hill is Pill Hill, and the second (Fairmount ridge is my name for it) and third are lobes of the Adams Point upland. These are parts of a larger structure that is central to Oakland’s character, an ancient Pleistocene alluvial fan. Here it is, marked “Qpaf” on the geologic map.

This walk takes in the leftmost edge of the fan, crossing two valleys of the Glen Echo Creek system which dissect the fan. The creek feeds the narrow west arm of Lake Merritt.

All right, here’s the route with the locations of the following photos.

Here’s the view up Hawthorne Avenue to the edge of Pill Hill. The land west of the fan is a modern alluvial flat with almost no topography to it beyond subtle levees along the modern Temescal Creek and the notorious filled-in marsh that once underlay the ill-fated Cypress Structure in West Oakland. The Pleistocene fan has fairly abrupt edges like this all around it.

As you go over Pill Hill and Summit Road on its spine, take a close look at the topography ahead of you. The near ridge is Fairmount ridge, made of Pleistocene alluvium, and the distant hills are Cretaceous and Tertiary sedimentary rocks. The eminence at the foot of the high hills is the older Franciscan block that underlies Piedmont and upper Rockridge.

The walk goes down into the valley of Glen Echo Creek. Brook Street is named for the Broadway branch of the creek, which is culverted under Mosswood Park and runs open to the sky in the backyards here. This shot is at the foot of 30th Street.

If you go upstream a little ways you can spot the culvert where the two branches join.

Next we climb the other side of the valley up a long flight of stairs, then turn right and follow the ridge top, along Fairmount Avenue, for a ways. A detour of stairways leads to Hamilton Place, at the toe of the ridge (the new Whole Foods place cut into that toe; unfortunately I never got a good look at the cut). From here we look across the next valley, which I might as well call Harrison valley.

This valley has a well-developed profile, but apparently it never had a permanent creek. The Oakland watershed map shows only a culvert here. Anyway, we walk up the far side of this valley and return west on classic Perkins Way, where we can look back at the other two ridges.

Back up on Fairmount ridge, we stroll up quiet Kempton Avenue, where this nice driveway wall of California mariposite lives.

Soon enough we find ourselves again at the steep edge of Glen Echo Creek valley. If you limit yourself to walking, Oakland is really quite a rugged place.

At the bottom is a precious remnant of early Oakland’s streambeds, Glen Oak Park. An old concrete bridge crosses the stream, and if you have time to stroll up and downstream there are some fine buildings here too.

I would be remiss not to mention that a little farther, at the foot of Piedmont Avenue, is a good sushi place, Drunken Fish.

This entry was posted on 29 December 2011 at 4:48 pm and is filed under Oakland geology walks, Oakland streams and water, the Fan. You can follow any responses to this entry through the RSS 2.0 feed. You can skip to the end and leave a response. Pinging is currently not allowed.