. Where I live
NOW, I have a sandy loam soil that is VERY sandy and not at all
suitable for
making cob.
If there are streams or rivers near you there may be clay there. As
you likely know, cob, and I suspect an oven also, is best with plenty
of sand in the soil mix so that the walls don't crack from shrinkage.
It seems increasingly the case, as we explore the designs of outdoor
ovens, that there are many materials and shapes that will get the job
done.