Why “Grand Round” is really really old in Oregon English
TLDR answer: Métis people!
The earliest occurrences of this phrase refer to the eastern Grande Ronde, as it’s now officially spelled. That’s the one in Union County, in northeast Oregon.
The reason for this is that northeastern Oregon was heavily traveled, visited by fur trade employees, and even saw some settlement, before northwest Oregon did.
The earliest occurrence of this eastern Grande Ronde that I have managed to turn up is in an 1838 book by Samuel Parker that’s also one of the earliest documents of Chinuk Wawa: This is from page 206:
A related detail from the same page is Parker’s mention of “Racine Amére [sic] east of the Salmon river mountains”, i.e. the “Bitterroot” country’s name in fur-trade era Métis / Canadian French.
Next I found an 1839 periodical “Missions du diocèse de Québec”, amusingly enough written in standard French but using the expression “Grand Round” in English. From page 19:
(‘They warned us that it was quite rough, and longer by 150 miles than the one that goes through the Dalles, Walla Walla, Grand Round, etc.’)
From an 1843 report to the city of Columbus, Ohio, on the Territory of Oregon, quoting the early missionary Reverend Spaulding (page 20):
Newspapers weren’t published in Oregon Territory itself until the mid-1840s (with Chinuk Wawa content of course). By then, western Oregon was the nucleus of Settler civilization in the region, so almost all “Grand Rounds” that we find in that era refer to the western Grand Ronde. (But in papers from eastern Oregon, from about Hood River eastwards, “Grand Round” still referred to the eastern one.).
Among the earliest “Grand Round” finds in print regarding Grand Ronde (the western one, in Polk County of modern Oregon) is an 1868 newspaper article from the state:
I’ve found about a hundred more occurrences of this phrase in historical Oregon newspapers.
“Grand Round” is sometimes written in old sources as GRANDE ROUND. Variations like this are common in the written record, showing that folks were aware of the French-language origin of these two places’ names.