Most of the climbing on this loop takes place on dirt roads—most notably the initial climb up Smuggler Mountain. Once on top of the ridge, the ride switches to singletrack. Here, a mostly mellow backcountry trail traverses up, down, and along the ridge crowned by 10,414-foot Red Mountain. Most of this traverse trail is smooth, flowy, classic singletrack bobbing and weaving through beautiful aspen groves and wide-open meadows.

The final descent down Sunnyside ratchets the difficulty up quite a bit, with more challenging rock features and a steeper trail pitch. Thanks to its south-facing aspect, gone are the massive aspen groves, with dry grass and low scrub oak replacing them. Consequently, the dirt on this section of trail is much drier, rockier, and dustier than other trail segments along this route. The mountainside here is also quite steep, with some respectable exposure on the downhill side of this narrow trail.

Sources: https://rootsrated.com/stories/aspens-biggest-best-mountain-bike-trails-in-aspen https://www.cyclelifehq.com/en/listings/305190-smuggler-to-sunnyside-loop-ride https://mountainbikefarm.wordpress.com/2012/09/16/smuggler-to-sunny-side-aspen-co/ https://www.youtube.com/watch?v=FYyHnmqU42E