With the heaviest rains I’ve seen in years, I checked out Dimond Canyon today to assess the power of the stream in it, Sausal Creek. The water was brown and impressive. It looked about waist-deep at most. I don’t know how this stream cut the canyon, which is a gorge more than 50 meters deep with stone walls. But I have a theory involving stream capture and movement on the Hayward fault, just upstream from the gorge. At various times, the fault has pulled the canyon past different watersheds. Perhaps lakes lay upstream, or landslides formed dams, that collected enough water to give the canyon a good downcutting once in a while. I hypothesize that the stream’s watershed was once quite a bit larger, perhaps even the valley now occupied by Chabot Reservoir. But the timing has to work.
There are at least two other gorges in the Oakland foothills that appear oversized to me: the upper reaches of Cemetery Creek, along Moraga Road, and the canyon of Peralta Creek in Redwood Heights, best seen from Rettig Avenue north of 35th Avenue.
It is recorded that the early loggers who stripped the redwoods out of the Oakland hills used to float their logs down Sausal Creek to the bay. All I can say is, there must have been a lot more water in the hills back in the 1850s, because even today’s deluge couldn’t have done that.
BTW see the Friends of Sausal Creek site.