This trail is one of the more fun singletrack trails on Mt. Lemmon. It provides excellent shade so even the hotter days are more comfortable here than on most other trails. The terrain is mostly easy to navigate with only a few rocky sections although it's a very popular area so you'll likely encounter a lot of other trail users.
Starting from the Marshall Gulch Picnic Area, head up the singletrack path just to the right (north) of the bathrooms. Watch out for some poison ivy near that trailhead beginning. The trail is very easy to follow the entire way. There is a creek nearby, and, depending upon the time of year, you'll have a few wet areas to navigate. While it gains over 500 feet in just over a mile and a quarter, it's never extremely steep in any one spot, so it's a comfortable climb to Marshall Saddle.