I would imagine that if a native source language is to be identified, it would probably be Chinookan.    From Wordnik.com.  [languagehat.com: ANYONE FOR SALISHAN?] Reference

There are words from English and French, and from various NW languages (including Salish and Wakashan languages) but the largest single source appears to be Lower Chinook (Chinook Proper) of the Chinookan family.    From Wordnik.com.  [languagehat.com: ANYONE FOR SALISHAN?] Reference

They appear not to have reached the Columbia River, being cut off by tribes of the Chinookan family, and consequently were not met by Lewis and Clarke, whose statements of their habitat were derived solely from natives.    From Wordnik.com.  [Seventh Annual Report of the Bureau of Ethnology to the Secretary of the Smithsonian Institution, 1885-1886, Government Printing Office, Washington, 1891] Reference

"The Chinookan people controlled the trade along the lower Columbia River.    From Wordnik.com.  [The Seattle Times] Reference

They are now classed as Chinookan.    From Wordnik.com.  [Seventh Annual Report of the Bureau of Ethnology to the Secretary of the Smithsonian Institution, 1885-1886, Government Printing Office, Washington, 1891] Reference

Chinookan tribes.    From Wordnik.com.  [Seventh Annual Report of the Bureau of Ethnology to the Secretary of the Smithsonian Institution, 1885-1886, Government Printing Office, Washington, 1891] Reference

Chinookan family 65.    From Wordnik.com.  [Seventh Annual Report of the Bureau of Ethnology to the Secretary of the Smithsonian Institution, 1885-1886, Government Printing Office, Washington, 1891] Reference

Chinookan family 65-86.    From Wordnik.com.  [Seventh Annual Report of the Bureau of Ethnology to the Secretary of the Smithsonian Institution, 1885-1886, Government Printing Office, Washington, 1891] Reference