Since no one else has responded, I'll chip in. I'm no expert, but we have patches of similar looking irises left over from the previous owner. They're prolific and carefree. You can see one in this pic in front of some black irises I planted two years ago, and another in the upper right. I haven't done any serious work on this patch of garden, so the rear section is full of irises like that along with daylillies. We have another patch behind our deck that's about 2 feet by 4 feet, filled in solid with these. I ought to thin it out, but it's been reliable and trouble free so far.

I'm not sure how that one in front of the black irises got there, but I'll be removing it as the others need more air.

We're just north of 128, so my guess is that these are just easy to grow irises in the area.