I'm rather certain you are looking at
Quercus kelloggii there - California Black Oak.
The bristle tips on the leaf margins will separate this species from similar leaves on white oak group species like
Quercus lobata. Your thorough selection of other images like the acorn and the bark further nail this down, and separate this tree from other California oaks.
You should have included a picture of the WHOLE tree, and pictures of more leaves since the leaf morphology may vary widely on a single tree. A single leaf or leaf cluster as shown is probably from new growth on a shadier portion of this tree. Leaves on a sunnier position - and especially leaves from dormant buds rather than from seasonal stem extensions - will look different from those you have shown.
All this information helps add up to good positive IDs. Here is a link to the Plants Database entry for
Quercus kelloggii.
California Black Oak (Quercus kelloggii)
