[Cob] Portland Oregon Cob source

[Amanda Peck]

I'm a long ways from you, but I hope this helps.

1) you don't want to use your topsoil for this anyway.  You may have a clay 
subsoil, but you may also not want that deep a hole in your yard.

2) when I was a kid (even farther away) people knew about veins of clay that 
were close to the surface that could be used for a) eating--reputedly for 
mineral imbalances, b) pottery or c) dying fabric a nice terracotta color.  
Road cuts are sometimes a good source.

People near you may know the same thing.

3)  I ended up buying a whole dump-truck load from the nearest gravel 
people, because there was a layer on top of the limestone that they wanted 
to crush for gravel.  They would have given it to me had I only wanted a 
loader scoop's worth in my pickup.  I have to buy sand too.

4)  push comes to shove, you might be able to buy some from either a brick 
manufacturer not too far away, or a pottery/ceramics supplier, one of which 
should be pretty local.  Depending on what you are buying, you too might 
have to buy sand.
.............
Michael writes (snipped) that he is

"having trouble with a good source of clay rich soil.  I
tried a couple of test bricks from my yard and the each failed.  All I need 
is
a couple of wheelbarrow loads (I think)."