This is an amazingly fun trail. It was built by the local high school mountain bike team and sticks to the natural contours of the canyon. There are three distinct segments on it, each bisect the Prairie Trail going through the park. If you're up to it, do all three for a lot of fun.
The A and B portions (to the northeast) are in the best condition on hard pack trail with some encroaching Russian thistle. The C portion which is the furthest out is in the roughest shape. It's sandier and has some damage from horses pock-marking it. Most fun ridden in the direction shown (east to west), but still a good ride climbing back through the park.
This is a great connector going from Redlands down to Live Oak Canyon Road, making a great loop connecting to the Carriage Trail in San Timoteo Canyon.