Symphyotrichum lanceolatum var. hesperium (Willd.) G.L.Nesom
Family: Asteraceae
common Western lined aster
[Aster hesperius A.Gray,  more...]
Symphyotrichum lanceolatum var. hesperium image
from USDA Plants website  
Etymology: Aster: from the Greek aster, "a star," describing the radiate heads of the flowers
Plants: erect, perennial, 2'-5' tall forb; long, colony-forming rhizomes
Leaves: only along the stem, usually entire, lance-like
Flowers: head 1/3"-1" wide with 20-40 blue to white rays; inflorescence long, leafy clusters with many heads
Habitat: moist; low areas
Conservation Status: Native