As stated above, the singletrack options along this trail are not legally open, yet many people have been known to partake in this option. I was once asked by a park ranger to get off the doubletrack trail. He was in his truck at the time so I didn't take his warning too seriously. Now if he had been on a bike, that might have been different. But a truck!! In an area closed to motor vehicles!?!?! I don't think so!! That being aside, I would suggest that any off-pavement excursions be kept to a minimum and courtesy should remain a paradigm to trail riding here. Keep in mind that some trails are posted as "No Bikes" while others are not. A bit odd, but so be it. The trail itself is easy to follow as it is paved, but as stated earlier you can turn around at any point. There are numerous rest stops, drinking fountains, picnic spots and whatnot along the trail so "fun events" are always a possibility. You may encounter equestrians, joggers, dog walkers, skaters and young families; so exercise caution. A hearty "hello" or "passing on your left" is always courteous. Posted speed limit along the trail is 15mph so watch yourself. Usually this is not too much of a problem, but every once in awhile an inattentive jogger, cyclist or child can cause disaster. Total elevation change is 440 feet over the 32 miles, however most of those feet come in the final grunt up to Folsom Lake in the last two miles. The lower 30 miles are flat. Since this is a paved trail it is open year-round however summertime temperatures can be into the low 100s, so plan accordingly. Spring and fall tend to be the most popular seasons, but any weekend can see lots of activity along this trail.
Starting at the confluence of the American and Sacramento Rivers, this trail heads east to Folsom Lake. The total distance (one-way) is 32 miles. You can ride any distance since it is an out and back ride. There is currently no "legal'"singletrack along this route, however that is under review within the Parks & Rec departments that oversee the Trail. However, you may be able to divert from the paved path up to the levees along the American River to get some dirt under your tires. The path on top of the levee is legal to ride on.
http://www.singletracks.com/item.php?c=1&i=70