[1] It sits on the south bank of the Fraser River, west of the smaller Chilliwack Mountain across the Vedder River mouth, and serves as a geographic landmark dividing the Fraser Valley into "Upper" and "Lower" sections.

[5] Its higher eastern reaches tower over Greendale, a community within the City of Chilliwack and is mostly wilderness; the mountain's summit, Sumas Peak, is located in this area, along with Chadsey Lake.

Farming,[6] gravel mining,[7] and logging[8] continue on the mountain to the present day.

The mountain protects McDonald Park, a dark-sky preserve, from the light pollution caused by the nearby cities of Abbotsford, Chilliwack, and Mission.

A common 19th Century spelling of Sumas was "Smess"; Simon Fraser's journal recorded the name as "shemotch".