It’s oak gall season!  I spotted the leaf below right in the middle of the trail, with galls from two different wasps.  The urchin gall wasp (Antron quercusechinus) makes the spiny pink galls and the crystalline gall wasp (Andricus crystallinus) makes the furry pink galls.  These wasps, in the family Cynipidae, lay their eggs in oak leaves (in this case a blue oak), and the eggs secrete plant hormone mimics which cause the leave to form the spectacular gall.  The larvae grow and feed in the gall for weeks to years, depending on environmental conditions, and then pupate within the gall and emerge as adults.

Continuing the oak theme, I looked carefully at oak regrowth along Cold Creek.  Interior live oak, an evergreen oak, is generally a more vigorous basal sprouter, as observed below:

Blue oaks, which are deciduous, generally do not resprout from their bases, but show regrowth in their crowns: