Coincidence? I think not.

The great observation on the Las Pilitas Nursery web site that in many cases (so-called) hybrids of blue oak and California white oak (a.k.a. valley oak) are more plentiful than pure examples of either "species" had me curious, so I looked up the ranges of both "species" in Oaks of North America.  Here's what I found.

Range of blue oak (Quercus douglasii)

Range of California white oak (Quercus lobata)

Beside the fact that the latter map was apparently rendered with a felt tip pen on the verge of drying out, the two maps look strikingly similar to me.

Hmmm... more hybrids than pure breds, and the exact same range.  Still sure we're talking about two separate "species" here?