Following directions given by a friend, we found it first just outside the park on the Little River Road which runs east to west from Olympic Springs Road to the Hurricane Ridge Road. There we found a large population of it right on the roadside, but the colony was past its prime and though we took pictures the flowers were a bit disappointing and we were sorry we had not come earlier.
Our disappointment was allayed by the fact that we found it again, this time in prime condition, as we were leaving the visitor's center at the top of Hurricane Ridge. We were in a bit of hurry to catch a ferry and I thought when I took photos that it was Platanthera unalascensis to which it is closely related. When I looked at my pictures later I discovered that it was this species.
Platanthera ephemerantha used to be identified as P. unalascensis but was recently separated from that species and given its own status. The most obvious difference between the two is the color of the flowers, unalascensis having green flowers and candida, white flowers or white and green. Otherwise both species are visibly very similar in plant and flowers and easily confused, as was my experience.
The flowers of both are said to have a faint scent but I have never detected it, though I've tried. The flowers are around half a centimeter in size with a tiny spur and are held on a spike that can grow well over 60 cm tall. Some of the plants we saw on the Little River Road were that tall, but the plants we saw on Hurricane Ridge were much shorter, around 30 cm, but were much more exposed.
The flowers are numerous, and though I did not count any of the spikes, certainly must be as many as 50-75 per spike, this putting on quite a good show. The leaves were still partly visible, usually two to four of them, and in the more exposed areas were short and upright while in the shadier areas along Little River Road were soft and prostrate and in both cases were starting to wither.