Muir's Hairstreak (Callophrys muiri)
or Juniper (Muir's) Hairstreak (Callophrys gryneus muiri)

Mt. Diablo State Park, Contra Costa Co., CA
23 May 1999

Mt. Diablo State Park, Contra Costa Co., CA
23 May 1999 (with backlight filter)

Mt. Diable State Park, Contra Costa Co., CA
23 May 1999