The Crystal Lake 4x4 trail accesses a handful of very popular hiking trails and ends at the lower of the two Crystal Lakes. A side trip to Francie's Cabin is now gated and only accessible on foot.
The trail is rough and rocky but has no obstacles. Where this trail diverges from the easier Spruce Creek Road, a fairly steep, loose, and rutted hill acts as a bit of a "gatekeeper". The trail is very narrow and has few places to pass. This requires more than normal patience and courtesy for the many hikers you will encounter. A few tall water breaks could drag on vehicles without good ground clearance. A large willow brush meadow at treeline all but guarantees some Rocky Mountain pinstripes on your paint.
Officially, the USFS allows camping at "designated dispersed sites". However, there are no designated sites along Crystal Lake. Despite several inviting spots, there is no legal camping on this trail.