This is not a well designed trail system so you need to make your own loops. You can easily ride 7 or more miles of loops. It is a combination of forest roads and a single track/motorcycye trails. Some sections include very steep climbs.
The Work Center road is right across from Placerville Church Camp. From Rapid City take Hwy 44 W (Rimrock) about 11-12 out from Canyon Lake Park. The turn off is a gravel road on the right hand side–2 miles past Johnson Siding. The road is also marked with a sign that says Pactola Work Center. Pull in about 100 yards and park in open field to the left of gravel road.