Little Sunflower
Helianthella uniflora
The genus name Helianthella means "little sunflower", but because it grows at higher elevations it is also known as the Mountain Sunflower.
The flower head is similar to the common sunflower. The leaves are narrower, and usually have three prominent veins on the under-side. A very similar species (Helianthella quinquenervis) has five veins.
At their blooming peak, these flowers cover large areas of the hills.