A search for Leo Gates here:
http://recorder.maricopa.gov/recdocdata/getrecdataselect2.as...results in a couple of possible hits. If this is your guy, he and his wife bought and sold property in Biltmore Estates (Phoenix) and then bought land in Scottsdale (suburb NE of Phoenix). You could also search for his wife to see if she later sold the Scottsdale property.
So probably he died in the Phoenix area and his obit would be in the Arizona Republic. Some info on searching for obits in this area is here:
http://www.phoenixpubliclibrary.org/pageView.jsp?id=9554. You can also try the State Archives:
http://www.lib.az.us/archives/If you decide he was probably in Scottsdale at the time of his death, you could contact cemeteries or mortuaries in Scottsdale.
Hope this helps.
Betty Jean