The Powder Alliance grew a little for 2016-17. Perhaps noting that Vail and the Mountain Collective include places outside North America, the new Alliance destination is in Japan. Kiroro has joined the party.
The idea behind the Powder Alliance is that people who buy unlimited season passes at Alliance ski areas get three reciprocal free days at each of the other places. Blackout dates vary a bit, with some allowing 7-day access non-holiday while others do not allow free days to be used on a Saturday.
The better known places include Snowbasin, Bridger Bowl, and Crested Butte. The others in North America are all out west: Angel Fire, Arizona Snowbowl, China Peak, Mountain High, Mt Hood Ski Bowl, Schweitzer, Sierra at Tahoe, Silver Star, Snowbasin, Stevens, Timberline, Whitewater.