On Tue, 6 Sep 2016 09:49:19 -0400, songbird wrote:

you have a substrate, for growing veggies you'll
need some compost (partially decayed organic materials)
and perhaps some clay to hold moisture. if the compost
is not very good you may also want to add some chopped
and dried alfalfa or other nitrogen rich plant based
material. let it sit (water it once in a while to keep
it moist) for a few weeks.

for other gardening/soil questions the rec.garden
groups still function. i'm very happy to go on at
length about such things.

worm composting is a very good way to keep such
gardens topped up with nutrients...

You bring up good scientific points in that I doubt there is much humus
(organic) material in this particular soil.

Bearing in mind the goal is to teach the kids science in the process, these
soils are Franciscan sediments, which are ultra mafic rocks which covered
the floor of the Pacific Ocean which were shoved fifty miles under the edge
of California about 30 million years ago, and then which popped up when the
Farallon Plate was consumed in this area (the Farallon Plate still exists
but only north of Mendocino).

Since it's all Franciscan sediments, it's really all the same "clayish"
sandstone. There's nothing else in these parts. Just that one clayish
sandstone (often termed "chert").

I'm trying to find a chemical composition description of Franciscan chert
but I wonder if you look at the soil in my pictures if it looks "decent" to
you?

I suspect it has far too little humus to be useful.
But I don't know that for a fact.

I just know that back east, the soil is black and filled with roots,
whereas out here, it's a uniform brown with almost no root matter and no
bugs whatsoever in it.

What is your soil like?
Is it similar to mine?