How to find a vein of clay?

Good Afternoon Permies!

Kind of an oddball question, I am on the hunt for wild clay.

While my property does not have clay, I do have access to a large hillside that goes down to a swampy area besides a river.

Before I start swinging my shovel around poking at random spots, anybody got tips and tricks for finding clay?

I just want to minimize the disturbance to the area if possible.

Got an auger? Taking a "core sample" is a lot less intrusive than digging in random places and will give you a good read on the depth and thickness of deposits.

My property is mostly caliche which is ground limestone.

Dear hubby found a 5' x 5' section of clay when we were building our garden.

When I asked dear hubby how did he find the clay. He basically said as Phil has suggested.  He also suggested looking at different areas when wet as the clay will be sticky and shiny looking.

He also said he could tell by the tractor tracks that were left where the clay is.