Forest Service 90a is a hiking, biking, and horse trail in Coconino County, Arizona. It is within Kaibab National Forest. It is 5.4 miles long and begins at 7,043 feet altitude. Traveling the entire trail is 10.9 miles with a total elevation gain of 1,312 feet. The Tiptop Tank (elevation 7,861 feet) reservoir can be seen along the trail.