Satyrium californica californica
These fly from about May through August in (seemingly) most of our mountains in southern Californa, and are not uncommonly found taking nectar - always with wings closed - along mid- to higher-elevation trails. They're single brooded, and while some sources have them using only Oaks, others list quite a few other common host plants as well, such as Ceanothus. According to Opler and Wright, Western Butterflies, p. 207, the explanation is that they use only Oaks in California and S. Oregon, and other plants elsewhere, suggesting sibling species.
Larvae are ant-attended.