On May 20 I was out orchid hunting in eastern Washington. After visiting two locations I visited a third location and found a mixed population of flowers some of which looked like the Mountain Lady's Slipper, Cypripedium montanum, other like the Northern Small Yellow Lady's Slipper, Cypripedium parviflorum var. makasin, and some that were obviously natural hybrids of the two, the Columbia Hybrid Lady's Slipper, Cypripedium x columbianum. These all grow together and may all be hybrids. The difference in the color of the pouches is the obvious clue. The Yellow Lady's Slipper is named for its deep yellow pouch and the Mountain Lady's Slipper has a white pouch, but many flowers in this population have pouches that vary from pale yellow to cream. Something in this population, probably the Yellow Lady's Slipper was very fragrant, too.
Small Northern Yellow Lady's Slipper look-alikes
Cypripedium parviflorum var. makasin
Mountain Lady's Slipper look alikes
Columbia Hybrid Lady's Slipper