Callophrys dumetorum perplexa
This distinctive green hairstreak (sometimes referred to as a Bramble or Lotus Hairstreak) can be common in the spring along mountain trails where deerweed and California buckwheat grow. It's an early flyer; my photos are from mid-February to late May. The upperside can be brown to gray, something apparent in flight, but they perch with wings closed.
The host in our area is deerweed, Acmispon glaber (formerly Lotus scoparius), and various buckwheats. Dumetorum is single-brooded, and overwinters as a pupa in the litter at the base of the host plant. Larvae feed from April-July. Taxonomically, these are a mess; expect the status to change.