to learn and which seemed practical in its application. This system, without the decimals, was initially referred to as the "Sierra Club grading system." Class 1 was a hike, and higher classes were more difficult and technical, going up to class 6, which referred to aid climbing. The fifth class encompassed a wide variety of levels of difficulty in roped free climbing, however, and the system began to be refined by climbers at Tahquitz Peak in Southern California. Fifth-class climbs were initially described as easy, moderate, or hard. This was found to be too coarse-grained, so Royal Robbins, Don Wilson, and Chuck Wilts came up with a decimal subdivision of fifth class consisting of 5.0, 5.1, and so on up through 5.9. This system was implemented in the early 1950s, with new routes and ratings at Tahquitz being described in mimeographed newsletters of the Rock Climbing Section of the Angeles Chapter of the Sierra Club. The system was originally referred to by names such as "Southern California" or "Wilts-Sierra system," but eventually came to be referred to as the Yosemite Decimal System, even though it was devised and standardized at Tahquitz, not Yosemite. The first systematic presentation was in the 1956 edition of Wilts's guidebook for Tahquitz. Mark Powell is said to have exported the system to Yosemite around the same time. The original standards for the fifth-class climbing grades were as follows: The original intention was that 5.9 would be the hardest possible free climb, with class 6 describing aid-climbing routes. Initially the scale was based on ten climbs at Tahquitz, and ranged from the "Trough" at 5.0, a relatively modest technical climb, to the "Open Book" at 5.9, considered at the time the most difficult unaided climb humanly possible. In later years, as gear and athletic standards in the sport became more advanced, many aid routes were "freed" (i.e., climbed without aid), and the class 6 label fell into disuse, so that 5.x could be a label for any technical rock climb, regardless of whether most people were doing it free or aided. By the 1960s and 70s, increased athletic standards and improved equipment meant that class 5.9 climbs from the 1950s became only of moderate difficulty for some, while new 5.9 climbs were much harder. Class 5.9 began to be subdivided as 5.9- and 5.9+. Eventually, climbers began adding classes of 5.10 and 5.11. In the early