Sp < Piman tu-uk-so-on, black base, referring to a dark stratum, in a nearby mountain
See Tucson in American Heritage Dictionary 4
A city of southeast Arizona south-southeast of Phoenix. A Spanish mission was founded nearby in 1700, and the present city was first settled in 1775 as a walled presidio. It became part of the United States after the Gadsden Purchase (1853) and served as territorial capital from 1867 until 1877. Population: 519,000.