This is Platanthera x estesii, a natural hybrid of P. dilatata var. albiflora and P. stricta. It was photographed along the Hurricane Ridge Road in Olympic National Park.
I find that really interesting about only one of the parents present. Do you think that means the pollenia are spread widly by their polinator, (I've read some orchids use a tactic of anoying the polinator so it flies a good distance before trying again) or because the hybrid has spread in it's own right from wherever both parents were together.
We have the same sort of thing happen in Florida...Platanthera chapmanii is believed to have descended from hybrids of P. ciliaris and P. cristata, but there are stable populations of chapmanii where only one purported parent is found nearby and the other is nowhere to be seen.