These linear mines were in some of the Prunus ilicifolia leaves that I was initially drawn to because of the many oval blotch mines (some with evacuated holes) they contained. I'm not quite sure what's going on here. I don't think the blotch mines were just the result of these linear mines eventually turning into big ovals; the blotch mines were quite regular, and most of them did not seem to have any linear mine associated with them. Even though there are blotch mines visible in these leaves along with the linear mines, I think that's probably just coincidence, since nearly all these leaves had oval blotch mines, while I only noticed a few of these linear mines.

See here for images of the blotch mines:



The Wikipedia article for Stigmella braunella says it mines the leaves of this plant, and says, "The mine is located on the upper-surface and is linear or serpentine and convoluted terminally and in this region frequently crossing itself or forming a blotch." Seems like a possibility?