When the PMDs are out and about on the Lower Yuba River there, a pattern that is often mentioned to imitate the duns are “Pinkies”. They work. But the pattern is really a pattern designed to imitate the “Epeorus” mayflies.
These yellow mayflies are important on many streams throughout the West. Here on the Lowewr Yuba they are around but not in great numbers. Even though it is not a well known insect, the hatches are not prolific and typically don’t occur on flat “technical” water. However, The Epeorus will be found in the swiftest portion of the river, and trout see enough of them to recognize them as food.
Their need for abundant oxygen and pollution-free waters restricts them areas of the river that has the best water quality. I believe that’s why they seem to be more prevalent in the upper stretch of the Lower Yuba.