Rainbows spawn 2-4 degrees lower than Browns. I lived in the San Bernardino area for 4 years and yes there are some areas that hold wild fish that spawn in the Inland Empire. I can also tell you that some places such as Lytle Creek have naturally reproducing populations of 2nd and 3rd generation stockers a mile or 2 from the heavily stocked areas. Big Bear L. has 2 creeks that have spawning runs in early Fall. Some of these fish might be "natural" fish, but I'd bet most, if not all, are actually the offspring of stockers. I've seen Rainbows over 5# caught out of one of these creeks. There are better places for numbers and average size than what I've mentioned but you'll have to do the research.

Tight lines,
Wade

Tight lines,
Wade