Aliases: Rainbow Iris, Sierra Iris
Hartweg's Iris and Western Blue Flag are nearly impossible to tell apart. It might help to remember that Western Blue Flag prefers wetter areas, grows taller (up to two feet high), and only comes in purple. Or it might not. The happiest approach, probably, is not to care - just call it an iris and consider the matter settled.
Blooms: May - July
Iris hartwegii etymology: Iris is named after the Greek goddess of the rainbow, a reference to the wide variety of flower colors found in the genus. Hartwegii is tribute to German botanist Karl Theodor Hartweg (1812 - 1871), who collected new species in California and various countries farther south for the London Horticultural Society.  
This Photo: Near the southern shore of Bass Lake, late May