I'd forgotten how much fun these trails can be on a Mountain Bike!
Good rules of thumb:
1) Bring plenty of water!
2) Print out a map of the trail loops, understanding that they aren't to scale, but good use for reference.
3) Bring a cheap comb and pliers for the inevitable invasion of cactus spines (in your tires and sometimes your face, ask me how I know)
4) Obey the one way only signs, please! Some people think it's cool to ride it in reverse- not only can it be dangerous but it tears up the trails.
There are two spots to park and enter Fantasy Island. The main trail head is at Harrison and Irvington- take Harrison south until it dead-ends at Irvington and there's a small paved lot for the riders. Tip: try not to leave any valuables in your car- take your cell phone, etc with you. There have been break-ins here, consider yourself warned!
The other entrance is off of Valencia, on the south side of the park. The pullout is a dirt lot but the entrance is fairly easy to spot. This will put you on the Bunny Loop and there isn't a map of the entire park at the trail head, so again, a map is a good idea.
This is officially State Trust land, so technically you need a permit (google AZ state trust land permit, you'll find instructions on how to obtain one). While not strictly enforced, the money from the permits does go to upkeep of FI.
There are several large loops: Lone Cactus, Christmas Tree, Bo's, Burro, Bunny Loop, to name a few. The trails are mainly flat single track with a few technical sections of steep washes, etc. There are tons of Easter egg "garbifacts" out there too.
There are about 26 miles of trails, most loops are on the map that's located at the trail head, some aren't (Rez, Fire, Bunny, Snake Dance, Bunny's Revenge). Basically, if you keep taking all of the right-hand options at the turnoffs you'll do all of them. Some trail heads are well-marked, some aren't, another good reason to tuck a printed sheet of the map in your CamelBak.
A quick review of the loops with which I'm familiar:
Lone Cactus Loop: The Main Loop of Fantasy Island. It's about 7 miles and has some steep sections right off the bat. Windy and fast, it's a lot of fun if you can hold your line. There's a really fun section toward the end called the Half-Pipe which is seriously a natural half-pipe in a small ravine. Stay to the left and you'll follow it just fine!
Bunny Loop: Exactly as it sounds. Flat and fast singletrack, but beware of the ever encroaching Cholla cacti on this loop.
Snake Dance: This is a FUN loop if you're into really fast and tight corners.
Bunny's Revenge: A combination of Bunny and Snake Dance. This one has a lot of fun downhill sections that aren't technical.
Christmas Tree Loop: You'll know when you're on Christmas Tree Loop, trust me. It's similar to Lone Cactus with fun decorations. :)
Burro Pit Loop: Contains the smaller off-shoot loop of the Dead Cow Loop. This, in my opinion, is the most technical of all the loops. There are some features like The Shaft (it looks exactly like it sounds- steep and really fast!) and the Over-Under, a cool obstacle that you ride over, loop around, then ride under in a little tunnel. You'll know when you enter the Dead Cow Loop- be sure to ring the bell for good luck!
Overall- plan on being out there for a few hours and if you're riding at dusk/dawn, bring a light. A ton of tun and great exercise! read more