Oakland Geology

The Redwood Canyon Formation sits above the Shephard Creek Formation in what’s called a conformable relationship, indicating that the two units represent a continuous span of time. The difference between the two formations is that where the Shephard Creek is fine-grained, the Redwood Canyon Formation is coarse, consisting mostly of wacke (dirty sandstone) and some siltstone. Neither of these rock types is rich in clay, whereas the mudstone and shale of the Shephard Creek Formation are pretty much defined by it.

Again, this unit dates from the Campanian Age of the Late Cretaceous Epoch, which extends from 83 to 71 million years ago. And again, it’s steeply tilted by activity along the nearby Hayward fault, although it was originally laid down in flat-lying beds. It holds up steeper slopes in Shepherd Canyon, being a stronger rock than the underlying unit. Elsewhere, the Redwood Canyon Formation turns into the Pinehurst Shale going upsection, but in Shepherd Canyon that unit does not appear, having been removed by faulting.

There’s another photo from this formation here.

This entry was posted on 8 April 2010 at 7:53 pm and is filed under Oakland sandstone/shale, Sausal Creek watershed. 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.