This section of Trail 100 is the most challenging which may force some to hike-a-bike in the more difficult sections. Note, there are many side trails which can be taken to avoid some of the advanced terrain.
From the parking lot head west towards the Hwy 51 underpass. Once you are through you'll start your first climb. You'll see a trail that forks right (North), but stay on the main trail up the side of the mountain. Once you reach to top, enjoy the views of downtown Phoenix to the south. The downhill is quite steep at the top so be careful and watch for others pushing their bikes up the hill.
The central part of Trail 100 consists of these types of short climbs and descents. You'll soon have another similar climb but the descent is not too difficult. When you get closer to Cave Creek Road you'll have one more steep descent. If you want to avoid this trail or dont want to climb it coming back, take the Trail 100 B option that will take you around the mountain instead.
After taking the Cave Creek Road underpass, you'll climb up to another ridge. To stay on the trail, follow it left (south) and climb up to another ridge. The downhill off this ridge is advanced, so if you want to avoid it you can take the access trail to Trail 25 (nice singletrack downhill) or the fire road which will connect back to Trail 100.
After you pass under 7th Street you'll reach another parking lot and visitor center. You can continue to ride Trail 100 to the western section or head back east.