The turquoise blue line painted on sidewalks downtown designates the Presidio Trail, a historical walking tour of downtown Tucson. The 23 sites are located in a loop around Downtown, from the Presidio San Agustín del Tucson wall south to Carrillo Elementary School, then northeast to the Hotel Congress and northwest to finish at the Telles Block, which is now Old Town Artisans. The 2½ mile trail covers most of downtown.
The bright blue turquoise color was chosen because it was the only paint that the City of Tucson had available that did not signify a water line or underground utility.
The Tucson Presidio Trust for Historic Preservation provides a map of the complete trail with numbered sites.
See also: Presidio Trail (aka Turquoise Trail), opens a new window
Sources:
"A walk along the Turquoise path." Arizona Daily Star. December 1, 2005. Page B1.
The Presidio Trail (PDF map) | TucsonAZ.gov
"Headin' out on the Turquoise Trail." Downtown Tucsonan. March 6, 2006. Page 7.
Find the information you need by calling the library's Infoline at 520-791-4010 or by sending your question to Askalibrarian.
