There's a large distance and difference in climate between southern California and the northern California and Oregon regions. These salamanders were originally from those norther California and Oregon regions
A part of the Ensatina Salamander population made their way through California at some point.
The weather is much warmer in southern California and the geography is also quite different as opposed to the northern California and Oregon regions. Because of that, the Ensatina Salamanders had to adapt to the climate and geographic changes.
You will find that the Ensatina Salamanders that live all throughout California are a bit different. Interestingly enough, they form a circle, with the salamanders inside it able to interbreed but the starting and end-point salamanders unable to. Thus making them a ring species