Deem Hills is one of the newer parks in Phoenix to open (2010) and as such a lot of people still don't know it's there. This means that it has much more of a secluded feel then some of the more well established trails around. It IS popular with mountain bikers though so be on the lookout for them as they like the more sparse feel as well. The main park entrance is in the Stetson Hills community with the nearest cross streets of 51st Ave and Happy Valley Rd.
Deem Hills is really 2 hills in one with a just under 6 mile circumference trail around both.
The trail itself is actually pretty nice and well cut through the desert but be aware that it can still be pretty loose in places, probably because it is so new. For an average hiker it's a very nice hike but for a beginner there are inclines that might seem a bit tough in places, especially if you head up to the summit (the Ridgeline Trail). The summit has a couple nice overlooks where you can take some pictures and is challenging enough to be worth the effort but this isn't really a workout type of hike. After all you're only gaining about 600 ft total.
Avoiding the Ridgeline Trail cutting through the middle on part of the Basalt Trail cuts about a mile off the distance making this side great for a quick 3 mile exercise.
It's not all about hiking :) Very nice facilities are here as well with a large parking lot, nice playground equipment, ramadas and restrooms, and several large fields. You may want to head out here just for a picnic with the family.
Great hike! I planned on the listed "3.8 mile", not sure how far off my gps can be but mine registered 5.2 miles. Went clockwise, up to summit and used "shortcut" to get back. Great views and not real busy. Visited on Dec 04, 2012