Apodemia dialeuca peninsularis
Flies mid-April through June in the Laguna Mountains. The San Jacintos are mentioned as well in the original description in Systematics, p.805-6. Two good places to see it: right off the highway at the Big Laguna Trail; and along Kitchen Creek Road at higher elevations. Both places have plenty of Eriogonum wrightii ssp. membranaceum, and these metalmarks should be easy to find in patches of the host in late May/early June. Koji Shiraiwa has mentioned (online in a forum) that there are virgulti similar to these on fasciculatum just a few miles from peninsularis populations in the Lagunas, but peninsularis doesn't fly in the autumn when virgulti flies again. Given research on other mormo-complex populations, that isn't surprising.
I don't know much about their life-cycle, but given that they are a single-brooded spring-flying member of the mormo complex, one expects a long larval development. For good photos of eggs and larvae, see Koji's photos at the Butterflies of America website.
Apodemia dialeuca peninsularis in the Laguna Mountains along Kitchen Creek Road. May 3, 2014.
Another Apodemia dialeuca peninsularis from the same day. These were plentiful wherever there was Wright's Buckwheat.
Apodemia dialeuca peninsularis in the Laguna Mountains along the Big Laguna trail. April 25, 2011.
This two peninsularis and the one below were flying early in a large patch of Wright's Buckwheat, their larval host, in the Laguna Mountains along the Big Laguna trail. April 17, 2008.
Apodemia dialeuca peninsularis, the Peninsular Metalmark. Note the almost total absense of white spots in the hindwind postmedian orange area, and the reduced basal white spots on the forewing close to the thorax. (Same day as above.)
While the members of the mormo complex are organized according to several criteria, including variation in the timing of broods, choice of host plants, diapause strategies, and larval development, wing characters can also be a factor. Below, I've placed a close-up photo of a wing next to descriptions from (or based on) the original descriptions of these subspecies. It isn't always possible to identify a metalmark based on what it looks like, but that can be a consideration along with where you are, the time of year, and the buckwheat plants the butterfly is associated with.
A. dialeuca peninsularis was described by John and Tom Emmel and Gordon Pratt in Systematics, pp.805-6 (in the species mormo, J. Scott has conveniently named the spring-flyers dialeuca).
Ground color: "brownish-orange to pale dull orange."
cm: Costal margin has "dark gray scaling fused posteriorly into the orange ground color."
ab, pb: anterior and posterior basal white spots greatly reduced.
asb, psb: anterior subbasal and posterior subbasal white spots reduced, and post. subbasal spot is about 1/2 the size of the anterior spot.
pm: postmedian row of white spots reduced, and spots 1, 4 and 5 greatly reduced or nearly absent.
m: marginal series small, reduced to specks in some specimens.
hpb5: hindwing postmedian series sometimes almost entirely absent, with 5th spot usually the most prominent.