Oakland Geology

This five-mile urban hike is more of a terrain-and-streams ramble than a bedrock ramble. It climbs over 700 feet, winding through the watersheds that freshen Lake Merritt and traversing some of Piedmont’s wildest land. Although I’ve walked the route both ways, I’ll present it here from west to east.

The route goes from the 19th Street BART station to the heart of Montclair on La Salle Avenue, where every 20 minutes the 33 bus will take you straight back to the starting point. Or vice versa.

The terrain map shows the watersheds and drainage divides along the way.

This route is just one of several good possibilities. I have a thing about views, so I favor ridge roads that thread the divides between stream valleys. There are three streams here: Pleasant Valley/Bushy Dell Creeks (Grand Avenue), Wildwood Creek (Lakeshore Avenue), and Indian Gulch Creek (Trestle Glen Road). My route follows Warfield Ridge, the divide between the first two streams. The eastern alternative would go up Longridge Road, the divide between the last two streams. And, of course, one could take the low roads that follow the three streams instead. I leave those as exercises for the reader.

For completeness’ sake, here’s the geologic map. The blue areas are bedrock and the other colors represent various bodies of sediment.

The interaction of geology and terrain adds interest to the hike, but truth be told, the elegant and extravagant residences along the way are just as attractive as the geology.

On Broadway and Grand Avenue, you tread the level ground of the late Pleistocene marine terrace (Qmt) along the foot of the Fan (Qpaf), the large body of Pleistocene alluvium that’s one of Oakland’s most distinctive geomorphic features.

To the right of the Grand Lake Theater, the tall red-and-white building stands on Warfield Ridge. Behind it is Round Top. Cut to the right of the theater and make your way to, then up Warfield Avenue. That building houses the Grandview Apartments, and it’s well named.

Warfield, as I said, is a ridge road. It goes up and down a bit, but mostly up.

If you’re like me you’ll want to catch your breath every now and then. There are views on all sides. Pause and enjoy them. To the left is Pleasant Valley.

To the right is Wildwood Valley.

And behind is where you came.

Stay on Warfield all the way to its upper end, at split-level Wildwood Avenue. Go on up Wildwood. Right after you skirt Witter Field, in the valley of Bushy Dell Creek, you’ll enter the Wildwood Creek watershed for real, and also finally encounter bedrock.

It’s humble stuff, Franciscan sandstone. But it makes good crushed stone, and it supported several quarries before Piedmont took on its current identity. Take a closer look at the terrain here.

South of the blue line, you’ll see four small gulches eroded into this rocky hillside. The third one was a rock quarry that was later made into Oakland’s Davie Tennis Stadium. The others remained unexploited and are now thickly wooded. All four have running water still, thanks to our wet winter.

I picked the route that goes through the rocky headlands between these gulches. Turn right off Wildwood to Wildwood Gardens, and wend your way through this elegant neighborhood, across the top of the Wildwood Creek watershed, to the start of La Salle Avenue. Stay on La Salle all the way to Montclair.

La Salle crosses a fairly flat part of Piedmont, then leads along the rim of Indian Gulch, the village’s greenest and most secluded district. The road then goes up the floor of the stream’s middle branch. At its intersection with Hampton Road is a newly refurbished sports park where you can (and should) refill your water bottle. Higher up this little valley is a former reservoir named Tyson Lake. You can’t get to it.

La Salle becomes pretty steep here as you climb out of the valley and crest the highest ridge at about 725 feet elevation. The change in grade is the clearest signal that the bedrock is changing, according to the map, from Franciscan sandstone to Franciscan melange. But you can’t see that, either — there are no exposures of the melange along this road.

Instead you can see the high valley of Montclair, home of the Hayward fault, as you finally start down. A walkway painted on the road helps keep the locals’ cars back. In that respect Oakland is more walk-friendly than Piedmont.

And here’s the view back from the end of the line.

The Hayward fault is mapped right on the corner of La Salle and Moraga. You’ll see the offset curbs much better on Medau Place, though, one block north.

This entry was posted on 24 July 2017 at 8:02 am and is filed under Oakland geology walks, 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.