Jalama Beach (1231)

Actually was thinking of slgwv since he is a geologist (I think)

slgwv is a geologist. (He confirmed this once to me.) I'm just a wannabe.

These are some really fascinating outcrops, though. I wouldn't mind poking around them for a while.

Though I typically don't have the patience for details needed for geology, I found this formation fascinating for two reasons. One was that if you looked further up the beach (see link below), the consistent slope of the rocks brought to mind the image of them as the edge of a huge saucer that had somehow been tipped up. The second was that the way the layers in the rocks look sort of like rings in a tree, like layers of sand that washed in with a tide and were then somehow immediately frozen in time.

Yeah, I confess; I am a geologist. Coastal California is very complicated (surprise!), and it's true, there _was_ a lot of subduction there. The subduction gets shut off, however, once the San Andreas transcurrent faulting gets established; then you have the plates sliding past each other rather than diving one under another. There's still lots of deformation, though, because the San Andreas is not straight. This has the effect (crudely) of locally causing pull-apart in some areas and compression in others. Basins form in the pull-aparts, and in turn fill with sediment. Some of these basin-fill units are also the source of the oil deposits in SoCal. Offhand these rocks look like that; deep-water marine deposits from sediment originating near-shore via so-called "turbidity currents." I remember there being classic deep-water sedimentary structures off SoCal, and these may be representative, but that's a WAG. In turn, the units deposited in the basins get deformed and can be uplifted as the motion continues, and that's why these could be at the surface now.

The San Andreas currently ends at Cape Mendocino, where there's a so-called "triple junction", and subduction is still occurring north of there. Hence the worry about risk from huge subduction-zone earthquakes as far north as Seattle. You don't see a trench off the Pacific Northwest because it's filled with sediment!