There are a few options for this trail. The most straightforward is to drive up FS Road 0079, which is generally passable in most vehicles, though somewhat steep in places. You can either park where Aspen Flat Trail (018)
comes out (FS Rd 5381) if you're planning to make a loop, or drive up to FS Road 0354. You won't make it up 0354 without a pretty capable 4WD vehicle, so most will park somewhere before the start of that road and start riding.
Remember to sign in at the kiosk at the trailhead. After that, you'll be on the main Shay Ridge Trail, a signed OHV trail - not allowed for vehicles larger than a Razor ATV.
Climb up one of the tire treads - it's a lot steeper here, and you'll work hard just to keep forward progress in spots. It's all rideable but quite steep in places with baseball-sized rocks littering the trail. If you can take your eyes off the trail, you'll be rewarded with beautiful views of the Abajos to the right (east) as you climb.
Reach the top of the climb as you turn fairly sharply left. Look for a clearing and picnic table on the left where you can hang out for a bit before starting your descent. This is essentially the point of no (easy) return. Descending is fast and steep and climbing back up wouldn't be a whole lot of fun. Completing the loop using Aspen Flat Trail (018)
is possible, but also a very long haul with lots of uphill hike-a-bike required on that trail.
Continuing on, you'll follow similar tire tracks down through aspens at first. It's beautiful during fall aspen season, and flowing for a short bit, then increasingly rocky until it goes through a super-loose, rocky, sandy section - still rideable, but be careful. It's certainly not purpose-built mountain biking, rather an OHV that you can ride with bikes if you choose.
Bottom out at a trailhead/parking area that marks the start of Aspen Flat Trail (018)
. Retrace your steps or complete the long, hard loop on Aspen Flat.