I spot murals in some out-of-the-way places, but I still wouldn't expect to see an exquisitely-detailed desert mural next to a nondescript freeway entrance ramp. Thanks to a tip from a man who takes the ramp from Irvington to northbound I-19 every workday, I headed out with my camera to find this gem:
It was worth the trip: finely detailed life-like plants and animals on the wall between an ugly onramp and a generic shopping center. As soon as you make the turn north from Irvington, be ready to pull off... and watch for potholes as you try to park. Here's another section (click to enlarge):
The mural is signed www.muralbyjos.com, but the website seems to be down. I found a listing, though: "Jos Villabrille, Tucson artist painting murals for home and business."
Update (August 12, 2011): Philip Synder has great close-up photos of parts of this long mural on his SmugMug page Irvington mural, Tucson.