Oakland Geology

This is the view from atop the old railroad crossing at Mountain Boulevard, overlooking the south end of Montclair Playground.

The Hayward fault is mapped running through here from about third base on the ballfield at the left across the field of view. Two trenches were dug across the fault right here in 1981, and Jim Lienkaemper, the US Geological Survey’s (therefore the world’s) leading expert on active faults in Northern California, found evidence that the 1868 earthquake ruptured the fault here. Here’s part of the map he published in 1992 showing this area (at the REN in WARREN).

The map is oriented so the fault runs vertically. The codes refer to evidence of active creep (C2) and vaguer evidence of creep (C3), geomorphic features of greater and lesser distinctness (G2, G3), and the trenches (T) I mentioned. “H2” means there was good evidence of fault motion in the last 12,000 years—in this case, historic motion. The little oval at the WA in WARREN is a sag basin, now a water feature in the park. (However, Lienkaemper wrote in 1999 that he had misinterpreted the terrain: it was railroad construction that created the basin.) From top to bottom, the two-letter codes are as follows: gi, gradual inflection in slope; rw, right-offset wall; sl, linear scarp; jo, opened joints or cracks in concrete; sc, scissor point (where the up and down sides switch); rb, racking/distortion of building; as, arcuate scarp; dr, depression in a right stepover (sag basin); rc, right-offset curb; so, surveyed offset feature. The other codes refer to specific publications. This level of detail is available for the entire length of the fault, and while the USGS considers its online database of 2008 to be the most current, I like the format of this older map, Miscellaneous Field Studies Map MF-2196

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