You can also drop off trees there. No indication of chip quantity limits:

"From January 4th through January 12th, 2016, the City of Tucson will have wood chips from shredded Christmas trees available for pick-up at Udall Park and the Los Reales Landfill. Bring your own container and take home some free wood chips for your garden."
tucsonaz.gov/treecycle

Maricopa drop off sites: phoenix.about.com/od/holidayevents/a/treedisposal_2.htm

Casa Grande: Christmas trees will be chipped at the landfill (5200 S. Chui Chu Rd.)
and made available, at no fee, to the public to use as mulch. Residents
requesting to receive the mulch are asked to bring necessary equipment
to load and haul the tree chippings. Sites: casagrandeaz.gov/dept/publicworks/recycling/tree-cycle/