Also known as DC, the "classic" in the name means it's good, but it also means it's crowded!
This trail is without a doubt the easiest and least technical ride in South mountain park. Crossing the many small washes that run down from the mountain adds some interest and fun without much difficulty. For the more daring rider, there are a fair number of optional jumps and drops as well. Remember to bring plenty of water, especially during the summer!
From the east parking lot, go south, keeping the mountain on your right. You'll see the DC trailhead leave from a map kiosk just after you leave the parking lot. Stay left as you go by the Marcos De Niza trail and follow the signs as you continue around the mountain toward the TV towers.
If you do get off the trail, don't worry too much. Chances are you'll reconnect to the main trail soon enough.