Here's a list of the Ikon locations for 2018-19 in North America. The list got a lot longer by the late fall compared to the original announcement in the spring. It was hard to keep up. The non-Alterra locations are independent resorts on the MCP or owned by Boyne Resorts, plus Killington (Powdr). There are also locations in Australia and New Zealand for the 2019 season that come from the MCP.
IKON Pass in N. America - Alterra in bold
California: Squaw/Alpine, Mammoth, June, Big Bear
Washington: Crystal, The Summit at Snoqualmie (Boyne)
Montana: Big Sky
Wyoming: Jackson Hole
Utah: Deer Valley, Alta, Snowbird, Solitude, Brighton (Boyne)
Colorado: Aspen Ski Co., Steamboat, Winter Park, Copper Mountain, Eldora
New Mexico: Taos Ski Valley
Maine: Sugarloaf (Boyne), Sunday River (Boyne)
New Hampshire: Loon (Boyne)
Vermont: Stratton, Killington (Powdr), Sugarbush
West Virginia: Snowshoe
Michigan: Boyne Mountain, Boyne Highlands
CANADA
Quebec: Tremblant
Ontario: Blue Mountain
Alberta: Lake Louise, Sunshine, Mt. Norquay (SkiBig3)
British Columbia: Revelstoke, Cypress (Boyne)