I'm not sure where you are in AZ, or how much landscaping there is near your garage, but vapor transmissions through a garage slab can result in significant moisture when you have a condition of dry air over moist soil with a porous concrete slab between them. The porosity of concrete is related to the water/cement ratio of the original mix, and garage slabs are typically a high water/cement ratio for ease of finishing, which results in a slab that offers very little resistance to vapor transmission. House slabs are usually placed over a vapor barrier such as visqueen, which helps stop this moisture from coming through.
In order to narrow down the source of your moisture, I'd suggest doing a shade tree version of a bulb test. To test a slab for the level of vapor transmissions, a clear plastic bulb is placed on the slab and left for a predetermined amount of time after which the amount of moisture which has condensed on the inside of the bulb can be measured. You can perform a similar test by cutting a 12" square piece of clear plastic, such as a produce bag from the grocery store (be careful that there aren't any tears or holes) and taping it down to your garage slab. Use a tape that will form a good seal to both the bag and the concrete, like packing tape or duct tape. Leave the plastic in an area where it won't be disturbed for a couple days. If you have moisture being trapped under the plastic, then you've got vapors coming up through the slab. You can then decide how to address the problem depending on the amount of moisture. Some floor sealants can be applied to the surface of the concrete (again, depending on the amount of moisture).
Try doing the test, then let me know if you've got condensation on the plastic and how much and then I can recommend some remedies for sealing the concrete if need be.