One of the metrics I include in the trip planning information is the “difficulty”, ranging from class 1 to class 5. What do these numbers mean? The short answer is that they’re part of the Yosemite Decimal System (YDS). These ratings don’t describe the amount of effort required; class 1 can be long and strenuous and class 5 can be quick and easy. Rather, the YDS describes the technical difficulty of the terrain. Detailed explanations are included below
Class 1 – Walk in the Park
Class 1 terrain is low-risk and doesn’t require much gear beyond footwear. That doesn’t mean the trail can’t be steep and difficult (from a cardiovascular perspective)! Most trails fall into this category. Counterintuitively, technical glacier travel is often categorized as class 1 or class 2 terrain despite the need for protective gear like ropes and harnesses due to the low to moderate slopes encountered.
Class 2 – Hands for Balance
Moving up into class 2 terrain usually means talus, scree, or steep snow. You’ll likely need to use your hands to maintain balance every once in a while, and the path may be faint or missing altogether. Trekking poles are a boon in this environment, and microspikes (or other traction devices) can be a lifesaver when this more complex terrain is icy.
Class 3 – Hands for Scrambling
Class 3 hiking and climbing introduces significant exposure (i.e., a high risk of injury during a fall due to steepness of the terrain) into the mix. Colloquially called “scrambling,” this kind of climbing requires both handholds and footholds but there are plenty of physical features for both; technical climbing gear is not required.
Class 4 – Highly Exposed Scrambling
Once you reach class 4 features, you should really be taking advantage of a rope, harness, and belay device. While there are plenty of natural features (i.e., handholds, footholds), the exposure is high and a fall could easily be fatal.
Class 5 – Legit Rock Climbing
Class 5 terrain is what most of us just call “rock climbing.” The obstacles are cliffs, and an unprotected fall will seriously injure or kill you. Ropes, harnesses, and all manner of other climbing gadgets are required for this kind of travel. This category is further subdivided, ranging from 5.0 at the easiest to 5.15d at the hardest.