Help identify snake I found

[tcarlow]

Looking for help identifying this snake I found on my back porch I've lived in my town for 20 years and caught lots of local garter snakes and such, but this one stood out as maybe something different, and definitely never had one that vibrated it's tail at me as he did! So I'm interested in knowing what it is, whether it might be native/wild or someone's lost/dumped pet.

It is about a foot long, found in western Oregon

Thanks for any and all info