Green’s Dictionary of Slang

Green River n.

SE in slang uses

In phrases

go up Green River (v.) [the Green River brand of knife, made in Texas]

(US) to die; thus send someone up Green River, to kill.

1872		Schele De Vere Americanisms 200: A very odd expression, confined, however, mainly to the mountaineers in the wilder parts of the Southwest [...] they say they send a man up Green River when they have killed him. The phrase had its origin in a once famous factory on Green River, where a superior kind of large knife was made, very popular among hunters and trappers. On the blade the words ‘Green River Works’ were engraved, and hence the mountaineers, using the knife to despatch an adversary, literally sent his blood up Green River.
1945		Tracks June 30/1: Four early expressions for conductor – superintendent, pilot, captain and master of the cars – have gone up Green River [DA].