Here's your clue!
Did you get it? If not, try here.
This afternoon I went back for more photos, this time with the macro flash to bring out some detail. It was terribly windy and these plants were getting blown over--not very strong compared to the surrounding field grasses.
So finally, we now know that this is Alfalfa, Medicago sativa. Thanks, Gretchen! It's a member of the pea family, Fabaceae, which Joyce correctly identified. Thanks, Joyce!