McMillan Spire is an 8,004-foot peak in the Picket Range of Washington’s North Cascades, within North Cascades National Park. Closely grouped with neighboring summits including East McMillan Spire, it stands beside the Terror Glacier in one of the range’s most rugged landscapes. That terrain was formed through uplift, faulting, the assembly of terranes about 50 million years ago, later volcanic activity, and repeated Pleistocene glaciation that carved deep valleys and steep relief. The peak also lies in a marine west coast climate zone where Pacific moisture brings heavy rain and snowfall, creating cloudy, snowy winters, clearer summers, and wet snow that can heighten avalanche danger.