The Sumallo River is located in southern British Columbia

British Columbia

British Columbia is the westernmost of Canada's provinces and is known for its natural beauty, as reflected in its Latin motto, Splendor sine occasu . Its name was chosen by Queen Victoria in 1858...

, in the Cascade Mountains to the east of Hope

Hope, British Columbia

Hope is a district municipality located at the confluence of the Fraser and Coquihalla rivers in the province of British Columbia, Canada. Hope is at the eastern end of both the Fraser Valley and the Lower Mainland region, and is at the southern end of the Fraser Canyon...

. It begins on the east slopes of Mount Payne, south of the village of Sunshine Valley

Sunshine Valley, British Columbia

Sunshine Valley, formerly named Tashme, is an unincorporated settlement and former Japanese Canadian internment camp on the Crowsnest Highway between of the town of Hope and the entrance to Manning Park in the Cascade Mountains of British Columbia...

. It flows north until it reaches Sunshine Valley where it turns southeast and proceeds into Manning Park. It continues southeast within the park, running alongside Highway 3

Crowsnest Highway

The Crowsnest Highway, also known as the Interprovincial or, in British Columbia, the Southern Trans-Provincial, is an east-west highway, in length, through the southern parts of British Columbia and Alberta, providing the shortest highway connection between British Columbia's Lower Mainland and...

 before eventually meeting the Skagit River

Skagit River

The Skagit River is a river in southwestern British Columbia in Canada and northwestern Washington in the United States, approximately 150 mi long...

, to the northeast of Marmot Mountain.

The name comes from the word Semall-á-ow given to Alexander Caulfield Anderson

Alexander Caulfield Anderson

Alexander Caulfield Anderson was a Hudson's Bay Company fur-trader, explorer of British Columbia and civil servant....

 by his Nlaka'pamux

Nlaka'pamux

The Nlaka'pamux , commonly called "the Thompson", and also Thompson River Salish, Thompson Salish, Thompson River Indians or Thompson River people) are an indigenous First Nations/Native American people of the Interior Salish language group in southern British Columbia...

 guide on an 1846 journey through the Cascade Mountains

North Cascades

The North Cascades are a section of the Cascade Range of western North America. They span the border between the Canadian province of British Columbia and the U.S. state of Washington and are officially named in Canada as the Cascade Mountains...

. This word is not from the Halkomelem language from local Sto:lo

Stó:lo

The Sto:lo , alternately written as Stó:lō, Stó:lô or Stó:lõ and historically as Staulo or Stahlo, and historically known and commonly referred to in ethnographic literature as the Fraser River Indians or Lower Fraser Salish, are a group of First Nations peoples inhabiting the Fraser Valley of...

 people, so it may be a Nlaka'pamuctsin

Thompson language

The Thompson language, properly known as Nlaka'pamuctsin or the Nlaka'pamux language, is an Interior Salishan language spoken in the Fraser Canyon, Thompson Canyon, Nicola Country of the Canadian province of British Columbia, and also in the North Cascades region of Whatcom and Chelan counties of...

(Thompson) word.