The locals have several theories about what is going on here.
The two favorites are:
1) These are "pods left by body snatchers" (quote from decedents of Rod Serling, who once lived nearby )
2) Giant rabbits live in that tree line and left these giant pellets.
I like "Giant Rabbits".

Whatever.....but I do give it the beans when I pass this field in the dark each morning.
Fish