I visited the Montclair Railroad Trail yesterday, while the sun was shining, and found it a delightful transect of some important Oakland bedrock, including this.
The Redwood Canyon Formation is part of the Great Valley sequence, a thick sequence of sedimentary rocks laid down between 150 and maybe 60 million years ago. It’s a late member of the pile, largely sandstone and siltstone in thick layers like this.
The Redwood Canyon Formation runs in a ribbon from the fault at route 13, roughly at Thornhill Drive, up and across the middle of Shepherd Canyon and over the canyon’s south lip into the canyon of Redwood Creek outside the city limits. Skyline Boulevard runs through it between the Skyline Gate staging area and Ascot Drive. Redwood Peak is held up by it. As the name suggests, it’s well exposed farther south on the other side of the hills on both sides of Redwood Creek as well as the lower part of Redwood Canyon along Redwood Road.