The hybrids looked like D. anglica, and were very uncommon. I assume
they were sterile F1 hybrids between D. rotundifloia and D. linearis
(very common in the area), rather than fertile D. anglica plants. In the
latter case I would expect D. anglica to be more common there, unless
recently introduced.
I just noticed that Schnell's distribution map for D. anglica shows
the range of this plant covering the state of Idaho down to the Utah
border!
Michael Chamberland