Above is a beautiful example of Plains Zinnia (Zinnia grandiflora, family Asteraceae). Having never seen this species before, I spent about half a day with my field guides and internet resources trying to figure out the name of this plant.
Plains Zinnia can be easily confused with Wooly Paperflower (Psilostrophe tagetina) which has very similar flowers. Both species grow low to the ground in dry calcareous soils on sloped or flat ground. In this image of Plains Zinnia, note variable scalloping at the ends of the petals, and the 3-6 petals per flower.
Plains Zinnia differs from Woolly Paperflower in the arrangement of its leaves. In Plains Zinnia they are oppositely arranged whereas they are alternately arranged in Wooly Paperflower. This character is clearly visible in this image. Additionally, note the brownish red hue to the disk flowers. This is another way to distinguish Plains Zinnia from the paperflowers.
These plants are perennial and will reappear from the same root stock year after year making them colorful additions to native plant gardens.