According to Byrd Granger in Arizona's Names: X Marks the Place :
"The name of the city of Tucson derives from that given to Sentinel Mountain by [Tohono O’odham] Indians, Ts-iuk-shan, referring to the fact that the base of the mountain is darker than its summit. Hodge also says the Tu-uk-so-on means "black base.”.... Indians customarily name locations for nearby landmarks, hence the name of the now-vanished Indian community at the base of Sentinel Mountain. Spanish pronunciation yielded Tuqui Son or the current Tucson."
Granger, Byrd H. Arizona's Names: X Marks the Place. [Tucson, Ariz.?] : Falconer Pub. Co. c1983. Page 630.
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