The start of trip begins just below the Stewart Lake Dam, there is a public launch site which also has free parking. Recommend getting an early start because 'tubers' start coming out around 10am but if a late start is what you are looking for then it is easy enough to maneuver around them.
The trip will take you through 1000ft cliffs, you will see many birds, deer, and even wild horses if you are lucky. There are many 'extis' but I suggest paddling the entire 14 or so miles to the Granite Reef Dam. Once you see the dam, look left for a yellow sign that reads 'Kayak Exit 3', that is the take out which is also free to access.
I recommend this trip in late August or September because the river is usually higher and moving at 1600cfs rather than the normal 700cfs. It is challenging for beginners and will still entertain experienced paddlers. The trip time (at 1600cfs) took about 3hrs 45min.
This section of the Salt River is just NE of Phoenix, many restaurants and lodging facilities to choose from.
Kayaks do not have to be registered in Arizona as of Sept. 2009. Check the Arizona BMV for updates.
From US10 take 202 loop, get off at North Powell Rd and go north. North Powell Rd turns into North Bush Highway. Continue on N Bush HWY and the public launch will be on your right.
Puts in and take outs are free and there are restrooms available along with free parking.
If you want to rent kayaks (sit on top), the Saguaro Lake Ranch is a great facility and they have a website.
Google Earth is a great resource to recon this trip, just type in Stewart Mountain Dam and look down stream for the public put in.