Stó:lō is a Chinuk Wawa name
The name Stó:lō for the lower Fraser River Salish people of British Columbia is quite possibly a Chinook Jargon word.
This idea hasn’t been floated before, so let’s look under the surface.
We know that Stó:lō /stá:ləw/ is the word for ‘river’ in these people’s language, which is also sometimes called Stó:lō, or else Halq’eméylem.
And due to the role of Oblate Catholic priests in making Chinuk Wawa widely used in BC, starting from the general lower Fraser area, stalo became a common word for ‘river’ in the province’s Jargon.
We see stalo frequently in the Kamloops region, once the “Chinook Writing” alphabet caught on in 1891. Here’s one of the earliest examples:
Kopit mokst sno Faraw iaka tlap drim kopa iht
kʰəpít mákwst snú (Faraw) yaka t’łáp (drim) kʰapa íxt
finished two year Pharaoh he get dream on one
‘At the end of two years Pharaoh had a dream one’pulakli, iaka drim iaka mitlait wik saia aias stalo,
púlakʰli, yaka (drim) yaka míłayt wik-sayá (h)áyás(h) stálo,
night, he dream he be.located not-far big river,
‘night, he dreamed he was by a big river,’iaka nanish sinmokst musmus drit ayu gris.
yaka nánich sínmakwst músmus drét (h)áyú grís.
he see seven cow really much fat.
‘he saw seven really fat cows.’
— from Kamloops Wawa #19 of 27 March 1892, page 76
I noticed Wikipedia making the same connection, from a different angle:
The first historically documented reference to these people as “the Sto:lo” occurs in Catholic Oblate missionary records from the 1880s. Prior to this, references were primarily to individual tribal groups such as Matsqui, Ts’elxweyeqw, or Sumas.
— from the Wikipedia article “Stó:lō”
I find just a few uses of the name for several decades afterward, for example in scare quotes as ‘Stalo’ Indians in a 1900 publication, and in a spelling ‘Stallo’ by the people themselves in a 1930s plaque:

OImage source: City of Vancouver Archives)
The Handbook of North American Indians hints at the rest of the story of how this word caught on as a standardized name for these tribes:
Stalo, from stá·ləw (Upriver [dialect]) or stál̓əw̓ (Downriver and Island) ‘river’, was adopted by [anthropologist Wilson] Duff (1952a:11 [The Upper Stalo Indians of the Fraser Valley, British Columbia]) for the people of Fraser Valley. The name appears as Stó:lō in the orthography used in the Chilliwack area beginning in the 1970s.
— from Wayne Suttles, “Central Coast Salish”, HNAI volume 7 ‘Northwest Coast’, page 474
But as I say, the previously unremarked link from the people’s own language to their being recognized by one of its words seems likely to be Chinook Jargon.
What do you think?
If I understand correctly you think that Stolo was originally a word meaning river in the Fraser River Salish languages. It was then adopted into Kamloops Chinook Wawa as a general word meaning river. After that it was used as a name for a specific upriver tribal group. I guess it is difficult for us to know for sure if the people always used this name for themselves or it was one of many names they used for themselves. But if they used it for themselves in 1930, then the elders must have known if it had already been used at least back to the 1880s. Interesting theory!
Yes! That’s an additional research question. I would definitely love to reach a reasoned conclusion about whether the Sto:lo people thought and spoke of themselves broadly as an ethnic group before newcomers labeled them, and if so, what they might have called themselves. If their cultural patterns were similar to what I understand of other Aboriginal cultures of our region, I’d guess the answer was no — that folks might most strongly have identified with their village and family. If such was the case, “Sto:lo” could well be a word we now use due to Chinuk Wawa’s influence.