Notice: The park has changed the trails so much that this doesn't really exist anymore.
The Estrella Mountain range is west southwest of the valley. You can see the Estrella Range behind and flowing away from South Mountain. It appears taller and it is. Unfortunately the Estrella trail system doesn't include the abrupt ridgeline that shoots up from the desert floor. Choosing some of the best terrain available I list this hike as a combination of trails. Check out the map photos below. Study the maps and be sure you understand your trip before heading out. The trailhead has several maps including topos posted. I suggest taking a moment to view them all. The route chosen follows the Rock Knob Buggy Trail out and comes back on the Rainbow Valley Trail.
Head out on the double width dirt road for the first two miles. This takes you right to Rock Knob on your left. The trail narrows to single track and passes though a shallow and wide saddle. Once on the other side awesome views of Rainbow Valley flow out in front of you. This is a great desert scene. The trail heads out towards the last mountain on your right to meet up with the Pack Saddle Historical Trail. Hang a left on this trail and head east. You are looking for a trail that heads up to the east side of Rock Knob. If you venture to far there is another trail at the ravine bottom that takes off north too. This trail is closed according to the park. It appears to be newly constructed by scouts in 1991. Anyhow heading up on the Rainbow Valley Trail you go up and over Rock Knob Saddle. The rodeo arena comes into view and you know you're on track. Continue down meeting up with the wide road near the end.
Trails spur off everywhere throughout this hike. My best advice is to study the topos before going. Take a compass and use it. A couple trips out here and you'll get the hang of it. The trails are poorly marked so stay away if this might be a problem. Otherwise get out and enjoy this Estrella excursion.
WARNING! Hiking and outdoor related sports can be dangerous. Be responsible and prepare for the trip. Study the area you are entering and plan accordingly. Dress for the current and unexpected weather changes. Take plenty of water. Never go alone. Make an itinerary with your plan(s), route(s), destination(s) and expected return time. Give your itinerary to trusted family and/or friends.