Phoenix is not know by it's mountain tops or high passes. In fact, Phoenix is known as "the valley" precisely because its generally flat. However, if you are ever in town for a visit, one of the quick, easiest and most pretty rides you can do is up South Mountain. And, as the name will tell, it's located just South of the center of the city.
On this ride I came from Tempe, which is the home of the largest ASU campus. There is a bike path that takes you along the Salt River all the way to Central Ave which is the most direct access to the mountain if you are in Phoenix. The bike path is brand new, wide enough for multiple bikes and quite pleasant. On the way, you get one of the best views of Phoenix Sky Harbor's Airport as it is literally located across the wash.
Once you enter the South Mountain park, there is only one road option for cyclist and cars. The top of South Mountain is roughly 2800ft which hardly classifies the climb as a Cat 3 but it's a challenging climb with a few pitches of 7-8% towards the middle and up to 12% on the very final few meters before the top parking lot.
Yearly there is a Time Trial up the mountain which is roughly 6 miles with an avg gradient of 3% but don't let these numbers fool you as this includes a section of downhill. The climb itself will put you to a (small) test with World Tour pro rider Brandon McNulty and worldwide known KOM hunter Phil Gaimon sharing the top spot of the Strava Segment clocking 16:30 for the ITT segment.
But South Mountain is know just know for it's one road to the top. It has roughly 50 miles of trails to explore on foot and it's actually one of the main hotspots for trail running in the city of Phoenix. So if you ever get bored of riding your road bike up, take the off road route as it's loads of fun too.