Glaucopsyche piasus piasus
There are eight named subspecies of the arrowhead blue, five of which are in southern California. The nominate subspecies now has a type locality of "Hwy. 70 at Soda Creek, E. Branch North Fork Feather River Canyon, Plumas County, California," as determined by John Emmel in the Systematics book, but its range extends into southern California (by my definition) into Kern County from the Greenhorns to Nine Mile Canyon. The photos below are from Sherman Pass Road. This butterfly was first collected by Lorquin during the gold rush and sent to Dr. Boisduval in Paris. It's one of many named in the latter's 1852 article on the exotic butterflies of California (excerpted below).
Arrowhead blues are lupine feeders and are single brooded, with an adult flight time that depends on elevation, but generally it's late March to June. Nominate piasus tends to be at higher elevations. As you go south and southwest from the Sierras to lower elevations, you find subspecies excubita and sagittigera, respectively*. Eggs are placed singly on the lupines - I find them on the flower buds. Larvae are ant attended, as shown below. They feed straight through to pupation and overwinter as a chrysalis.
* According to Ken Davenport's Emmel Update, subspecies excubita and sagittigera meet around Frazier Park (Kern Co.) and Lockwood Valley Road (Ventura Co.).