Sumas Peak is the high point of an area labelled as "Sumas Mountain" on the 1:50K map. It is a large, wooded massif located right in the middle of the Fraser Valley on the south side of the Fraser River. Don't mix this "Sumas Peak BC" with a Sumas Mountain USA, which is 24 m away in Washington. What makes it confusing is that the Canadian massif is also referred to as "Sumas Mountain". For example Sumas Mountain Provincial park.
Suburban housing developments from nearby Abbotsford have crept up the mountain's southwest flank, but the northeast portion of the massif remains largely untouched save a road that leads to microwave towers near its summit. The swampy Centennial Trail crosses the massif from west to east.
Geologically, Sumas Peak is composed of the same rocks as the summits to the north across the Fraser, except for the sandstone around McKee Peak. It's separated from the Cascades by the Vedder Mountain thrust fault and Sumas Prairie graben. Geographically, however, Sumas is part of neither Cascades or Coast - rather, it is part of the Georgia Lowland - because it is on the "wrong" side of the Fraser to be a Coast Mountain. The gentle southwest slope of Sumas Peak is a remnant of the original peneplain which predated the formation of the Coast Mountains.
Name Notes: Don't mix Sumas Peak (BC) with Sumas Mountain in Washington. The Halqemeylem name for Sumas Peak BC is Teq'qeyex which means "gap where chunk broke off". During the Great Flood, canoes filled with people were tied to this mountain; the canoes broke off and floated away to the south - Sto:lo Atlas.