This abandoned railway started out as part of the Maricopa & Phoenix Railroad, see The Mesa Branch.
This spur survived for about 8 years after the 1933 abandonment of the Mesa branch. It ended just past the top right arc of the line, just to the east of the former North Mesa Station. While this entire line was officially abandoned, the spur still served customers at the southern end of the route near its junction with the mainline; even today, a single customer still exists, and the spur is still in use to 3rd Avenue and South Sirrine.
Thanks to Greg Rose for contributing information about this route.