These long spires are the flowers of the appropriately-named "June Grass" (Koeleria macrantha). June Grass is a perennial in the Poas family and grows 18-24 inches tall, pushing these green-white heads above the surrounding Bluestem and Indian Grass during this month, but then they'll be overshadowed later by those taller grasses. Named for a German botanist of the 18th century, Ludwig Koeler, June Grass grows in sporadic tufts over the native prairie grass and blends in with the airy white inflorescence's of PrairieYarrow and Philadelphia Fleabane.
Another brownly-blooming denizen of the prairie right now is Texas Bluegrass (Poa arachnifera). This dioecious grass chooses whatever sex of flower it wants to display and gets right down to it in the early summer. The species name refers to the long white hairs of the spikelets which are said to resemble a spider web. I don't see the resemblance, myself.