Don't get me wrong Steve, but the pottery, even though it is plentiful now, will be gone in the future if it doesn't get picked up. Keep in mind, you only see what is on the ground, there is much more in the ground. Repeated farming operations, freeze and thaw etc. will eventually turn all the pottery to dust size particles.
I pick up all the pottery I find here in eastern South Dakota, and in the last 5 years, I haven't picked up enough to fill a cool-whip bowl, (something I know you could do in under an hour out there) and most pieces are less than 1/2" x 1/2 inch. I know that we have been working the soil over here much longer than you guys have been over there, so it is just a matter of time, and your pottery shards will look like our pottery chips. I'd be picking some up if I were you.
Joel