Skinner's Hairstreak or Loki Juniper Hairstreak
Loki is a colorful hairstreak associated with California Juniper - Juniperus californica - in such southern desert locales as Anza-Borrego (San Diego Co.) and around the Santa Rosas (Riverside Co.). It's double-brooded, with adults emerging soon after the butterfly season begins in March, and then again in the early summer. I know it from Cactus Spring Trail, where it is easily found during its flights.
My dates for Cactus Spring Trail are skewed towards the March-April brood because I usually visit earlier in the year, not during the summer heat in June or July when the second brood should be emerging. In 19 visits with sightings, the pattern is that loki flies there beginning in mid-March through April, with worn individuals in late April and well into May. The second brood begins emerging in May, overlapping the previous generation somewhat. For the second brood, I have photos of fairly fresh loki from May 14, 2006, and a very fresh individual from May 23, 2016.