Oakland Geology

Chimes Creek is the second of the three streams in Mills College. It is said to get its name in reference to the college’s church bells. The sound would have traveled up the creek bed to the meadows behind Millsmont ridge. Today the freeway noise drowns them out. Here’s how it looked to the mapmakers of the U.S. Geological Survey in 1897—it’s represented by the dashed blue line in the middle. Below that is the same patch of land in Google Maps as of today.

The land has been changed substantially in the last 118 years, but the creek continues to drain its catchment. Let’s look at the changes from the top down:

• The headwaters have been filled and paved and are now occupied by Viewcrest Drive.
• The Leona Quarry removed all the overburden below a short stretch of the upper creek, exposing bare rock.
• The flats beneath have been leveled and developed, and the creek is culverted.
• Seminary Avenue has been widened and straightened, putting more of the creek underground.

All of these changes have added to the runoff seeking to enter the creek while constricting its course. A stream will respond by running higher and faster and eroding its banks.

I haven’t yet visited the highest part of the catchment. Here’s a look at it down Altamont Avenue.

The original creekbed is high above the left edge of the quarry, and the creek ran toward the lowest part of the foreground. Next is the view one block over, at Delmont Avenue and Hillmont Drive looking north. The creek comes out of its culvert behind the houses on the left.

I should note that the Hayward fault is mapped running right up the valley to this spot. That’s an important detail that no one seems to acknowledge. For my purposes in this post, it means that Chimes Creek is probably cutting downward through fault gouge, the finely ground material that faults make all over California.

Farther downstream, this is looking across the creek valley at Nairobi Place. The sides are quite high here because the stream cuts downward rather strongly.

The presence of the Hayward fault also explains why the right (opposite) bank of the creek valley is elevated above its surroundings—it’s not a levee, but rather a pressure ridge. Farther downstream along Oakdale Avenue, the valley is at its deepest.

The lots along Hillmont Drive, across the creek, are being undermined as the invigorated stream does its work.

I’ve love a good look at this material, but I’ll probably never get the chance. The geologic map shows this area as the northernmost splinter of the San Leandro Gabbro.

The creek enters a culvert under Seminary Avenue here . . .

. . . and emerges here on the grounds of Mills College for a couple hundred feet. Then it enters its last culvert and joins Lion Creek underground.

The Chimes Creek Neighbors site has thorough documentation of the human squabbling over this much put-upon watercourse. The neighbors know it as a permanent creek, although the 1897 map showed it as intermittent except for its lower reach on the Mills College campus. I suspect that the land-use changes of the last century have turned it into a permanent and more powerful stream.

This entry was posted on 7 February 2015 at 1:28 pm and is filed under Hayward fault, Oakland streams and water. 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.