Mournful Duskywing,White-edged Dusky Wing, Erynnis tristis

Erynnis tristis, Mournful Duskywing, or White-edged Dusky wing lives on oak leaves.

This is one of those pesky caterpillars you find on coast live oak trees. The males set at the top of hills and wait for the females to show up.  Females of this species  fly up to hilltop to mate. Other similar species do not.
You'll find this butterfly on a variety of flowers in the areas where there are oak trees.