The San Pedro Riparian National Conservation Area was established in 1987. The trail system is fairly young and under used. It is rich in history both modern and archaeological. It is broken into three separate networks.
If you are willing to ride outside the box however (ride pavement) it would be possible to easily ride from one section to the next. Most of the rides are suitable for the beginner although there are certainly some sections that qualify as intermediate. A down side to many of these rides are the inevitable sandy stretches. The individual rides described are all fairly short but could certainly be combined in many ways. Starting from San Pedro House, for instance, you could ride to the Waters Road trail head in Palominas then return by way of the Miller Back Country Camp and go North to the Escapule trail head and back to San Pedro House for a ride of over 30 miles. Starting from Fairbank you could ride to the Charleston Road trail head then return and ride all the way to the Cienega trail head in Saint David and back to your car for a very challenging ride exceeding 40 miles. A ride on my wish list is to be let out at the Palominas trail head and have a friend waiting with a van at the Northern trail head in Saint David which would be a nice 38 mile one way ride.