Wacke is pronounced “wacky.” It’s a name for coarse sandstone that contains a lot of junk: clay, rock fragments and minerals other than quartz. This is a closeup of wacke from the Oakland Conglomerate from Shepherd Canyon (more about that below).
The geologist looks at this and envisions a young mountain range with rivers carrying its coarse debris offshore, where a submarine canyon carries the stuff into a deep basin. Something like the Russian River, or the Mad or Eel Rivers, and a canyon like the Monterey Canyon. This rock formed about 70 to 80 million years ago, in the Campanian Age of the Cretaceous Period.
I’m going to be giving a talk on March 17th to the Friends of Sausal Creek about the geology of its watershed, which runs through Fruitvale and up Shepherd Canyon and the slopes of Joaquin Miller Park. Everyone is invited and there is no charge. It’ll be at the Dimond Library, 3565 Fruitvale Avenue, from 7 to 9 p.m. I’ll be bringing rocks and showing Powerpoints and possibly being a little wacky. What else have you got to do the night of St. Patrick’s Day?