Skiing is the godmother of extreme sports. It has been around for 7,000 years. However, it has never been more popular than it is right now. In part, the popularity of downhill skiing is due to the fact that you can go faster on skis than you can in any other motorless or flightless sport. The steeper the terrain, the faster you can go. Equally as exciting, the steeper the run, generally the more challenging. For safety reasons, ski areas demarcate the difficulty of each run with a sign containing shape and color symbols. There are four "hardest" rankings intended for advanced and expert skiers only.
A single black diamond demarcates a run that is for advanced and expert skiers only. Black diamond runs can be either groomed with a snowcat or left natural. That means "blacks" are often strewn with moguls. Although steep, black diamonds are rarely inclined to the point that if you fall you will slide to the bottom of the run. There are exceptions, however, because black diamond runs range in difficulty from state to state and from ski area to ski area. Regardless, blacks are certainly much more challenging than beginner and intermediate runs. A good example of a black diamond run would be the mogul runs used for Olympic freestyle competitions.
Double Black Diamonds
A sign with two black diamonds next to one another is an indication of an expert-only run. These slopes are so steep that grooming them is difficult and, as a result, not a regular maintenance objective. Often times these runs are so steep that if you wreck or a ski ejects, particularly if the conditions are icy, there is a good chance you will slide to the bottom of the hill. If you think about the trees, rocks and other obstacles on a mountain -- the consequences can be serious. Until the mid-2000s, "double blacks" were the hardest runs possible.
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With the addition of lights to ski areas, another type of black diamond has been introduced -- the "night black diamond." It's demarcated by a black diamond with an orange boarder around it. Night blacks are usually black diamonds during the day as well, so the orange boarder is an indication of the fact that the run has lights for night skiing, not an indication that it's easier to ski during the day. If a reflective orange boarder doesn't appear at night as you ski up to the sign, the slope isn't open for night skiing.
Double Black "EX" Runs
Some of the country's more extreme ski areas, particularly those in Colorado, add an "E" in the first diamond and an "X" in the second of a double black to indicate a run that is so steep that it's at the upper limits of even most experts' capabilities. These runs are so steep they are never groomed, which means that the terrain is guaranteed to be more extreme than even that found on most double blacks. Losing a ski or falling on a double black "EX" run means your odds of getting injured are high. These runs are often so steep that they aren't even used in National and World Extreme Skiing Competitions. They're generally just narrow chutes, sometimes no wider than 7 or 8 feet, are long, have a high potential for avalanches and aren't regularly patrolled by the ski patrol.