That cal king x gopher was found in northern calif on acres of private land that has been untouched. So there was no chance it was a man made hybrid. It was also found by Brian Hubbs who is known for being a bit of a locaity guy. His new book will probably have pics of this snake.

There have been others found as well as natural hybrids in other parts of the country. It's not uncommon. Snakes evolve and they will breed with each other. Cornsnakes X kingsnakes, X other ratsnake species are even more common in the east coast. It is a common theory that most of the north american colubrid came from the black milks in central america.
Also with made made hybridization there is a great number of species from two widespread geographical locations that have recessive genes that ARE allelic with eack other. The chances of this is almost zero unless they originally shared these genes and evolved from each other.
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"Yeah ya told me, and ya wrote it down too. But how the hell am I supposed to remember!"