I nearly edited my comment below to add a mention of Pine Mountain but selfishly (…yes I’m sorry) wanted to keep it obscure in the hope that it’d be less crowded when I visit it myself periodically.

If I’m going be less selfish, I should probably mention that my next favorite stargazing spots are Star Valley, WY (yes, named for the celestial views); the high mountain plateaus (8,000-10,000ft+ altitude) between Bozeman, MT and Red Lodge, MT; and Central Idaho (Sawtooth or White Cloud Ranges).

I haven’t made it to Steens yet, thanks for the prompt ;)

Happy Stargazing!