Indian Bread-root, Psoralea esculenta

Interesting plant, I'm not familiar with it. Unusual how it stands up so straight.  Being curious about the common name I googled, this wikipedia page explains its use in making flour.  There is also a closup of the flowers, which enlarges several time, up to a bee's-eye view.
http://en.wikipedia.org/wiki/Psoralea_esculenta

Further investigation, shows that this plant should be called Pediomelum esculentum these days.
http://plants.usda.gov/java/profile?symbol=PEES&photoID=pses_001_avd.tif
http://wisplants.uwsp.edu/scripts/detail.asp?SpCode=PEDESC

On the USDA site, I was taken with how attractive Pediomelum megalanthum is, take a look:

Pediomelum megalanthum (Woot. & Standl.) Rydb., Intermountain Indian breadroot
http://plants.usda.gov/java/profile?symbol=PEME7&photoID=peme7_001_ahp.jpg
http://plants.usda.gov/java/largeImage?imageID=peme7_001_ahp.jpg
http://plants.usda.gov/java/largeImage?imageID=peme7_002_ahp.jpg

Excellent info, Mark.

This particular photo from one of your links shows what I noticed (but couldn't photograph clearly with the Blackberry) - the flowers on a single flower stalk (or different flower stalks on the same plant) can vary from purple to pink to yellow (or puce).

http://wisplants.uwsp.edu/scripts/bigphoto.asp?bigphoto=PEDESC_NOLL2.jpg&taxon=Pediomelum%20esculentum%20(Pursh)%20Rydb.&phog=Christopher%20Noll&spcode=PEDESC

I would have expected the multicolors would be due to flower age, and the Wisconsin site pic seems to support that.  However your first photo, Lori, does not.  On the older clusters, even the new flowers are the "other" color.

I've been on the watch for this species on my prairie walks for quite some time, but have yet to find it.  It's even been cataloged on a couple of the prairies I've been to.  To date, I've only seen a relative, Pediomelum argophyllum.

I have seen neither but I have heard of the genus Psoralea!

Silver-leaf psoralea is a familiar one from when we used to visit Theodore Roosevelt National Park in North Dakota, a fantastic badlands, grasslands and riparian setting.  Beautiful leaves.

The leaves of Pediomelum argophyllum are indeed beautiful, so smooth and silvery, worth growing for the foliage alone!