Formerly present on the Sacramento Valley floor but now extinct at both North Sacramento and Rancho Cordova. Common in foothill woodland in the lower Coast Range and Sierra Nevada , usually seen in good numbers visiting flowers of California Buckeye. This and the California Hairstreak are the first species of Satyrium to emerge in the foothills. There is one brood, from the end of April to late June. Females may have quite a bit of orange above.

An east-slope species, abundant and breeding at Sierra Valley, straying to Donner (where no hosts are present). It flies in late spring-early summer (May-July) and visits Eriogonum nudum, E. umbellatum, Milkweeds, Alfalfa,Yarrow (Achillea), Yellow Ivesia and other flowers - sometimes in great numbers and often in the company of the Juniper Hairstreak. The host is Bitterbrush or Deer Brush, Purshia tridentata (Rosaceae).

This species has a variety of ecological races, or ecotypes. On the floor of the Sacramento Valley, where it is nearly extinct, it feeds on Valley Oak (Quercus lobata) and visits Hoirehound (Marrubium) and Dogbane (Apocynum cannabinum) flowers almost exclusively. Valley specimens are lustrous and sharply-marked beneath. Foothill ones, which seem to breed on a variety of oaks, average slightly smaller, less lustrous and less sharply-marked; they are usually very abundant and visit California Buckeye very heavily.

This is interpreted as the entity occurring on Castle Peak and on a tiny area of Donner Pass. It is larger and darker than subspecies semiluna, and the males lack a stigma. Males perch territorially,often on the matted ecotype of Bitterbrush (Purshia) growing along the ridgetop between Basin and Castle Peaks. Females walk a lot. Both sexes often visit Mule's Ears (Wyethia mollis) flowers, as well as Sulphur Flower (Eriogonum umbellatum). One flight in the second half of the alpine season, generally July-September.

This subspecies is a little smaller and grayer than nominate fuliginosum, and the male has a stigma. It occurs widely in the central and southern Sierra and in the northern Great Basin. There is at least one population in Siera Valley which, however, has only been found once at our study site. Males perch atop sagebrush in the midst of shrub-steppe. Both sexes can be found far from any blooming nectar sources, but they do visit Yarrow, Brassicaceae (e.g. Cardaria pubescens) and Sulphur Flower (Eriogonum umbellatum).

Usually common to abundant where found, the Sepia Hairstreak emerges last among our Satyrium species and often flies quite late in the season, especially at higher elevations. Like all the Satyrium it has only one brood a year, wintering as the egg. There is no significant variation in or among our populations. Visits flowers, including Wild Buckwheat and Rabbitbrush. The hosts are various species of Ceanothus. June-July at Gates Canyon and Washington, mainly July at Lang, and August to October(!) at Donner. Males are territorial perchers in late afternoon.

Distributed from sea level to near tree-line, but mysteriously absent from many places where its hosts are abundant. On the other hand, local colonies are very persistent-in some cases seemingly centered on individual trees. This species was incredibly abundant in the Sacramento Valley in the 1970s but is now teetering on the brink of regional extinction for no obvious reason. Its numbers also seem to be decreasing in the mountains.

On the transect, this species is disjunctly distributed, occurring in Gates Canyon, where it is uncommon, and at Sierra Valley, where it is abundant. Both populations feed on Mountain-Mahogany (Cercocarpus): Gates on the foothill species, C. betuloides, a chaparral shrub, and Sierra Valley on C. ledifolius, found in rocky habitats in East slope shrub-steppe and often at or near tree-line in arid climates. The Sierra Valley animals, especially females, are larger than at Gates. There is one brood, in June-July at Gates, July-August at Sierra Valley.