What area should I get soil for dam? I assume Cec is red clay but not sure I'm tring to attach a soil map pic not sure if it is working

It posts but I don't know what the acronyms mean. In general, shoot for about 60/40 clay/soil. It can vary though. Silt, rocks, sand, gravel should be avoided.

Admittedly, loam is partial sand but is a good mix with the
clay.

Pure clay cracks when it dries.