With the loop being either all uphill or all downhill, the Guardian and Annie Bidwell Trail (formerly known as the South Rim) is recommended for advanced riders in great shape.
Guardian Trail is an extremely exposed single-track, featuring cliff edges in some areas and amazing views of the gorge.
Annie Bidwell Trail (South Rim) Trail is extremely rocky and very technical, with several drop-offs of more than 4 feet along a washout. Start down a steep fire road at 10 Mile House Trail, take the left turnoff to ride down Guardian Trail.
When Guardian Trail ends at South Rim Trail, bear right (north) for a steep descent to the Annie Bidwell Trail. Keep right for the Ten Mile House Road and back to where you began.