Pulsatilla vulgaris (European Pasque Flower). I love this flower! In it's native form it is usually the first flower to bloom in the Spring, usually March. It prefers an east-facing slope to take full advantage of the warm Spring sun. It is a reseeder and a good naturalizer.
The native Pasque Flowers that grow in the foothills of this area are a much lighter color but I have not been able to purchase them anywhere.