Alaskaflyer has it dead on!
The most deadly issue is speed. A slower aircraft gives you a little bit more time to evaluate situations, make decisions, and execute escapes. There is a HUGE difference between 105/110kts and 145/155kts getting you into trouble, and what it then takes to get you out of it! If you are flying a HP aircraft, then use it accordingly. Get up high to an MEA (16,000' in CO) and go over the mtns. But for those not able to get up to those altitudes, there are still ways to get through the mtns safely.
I have seen the results of 182's (turbo's and non) and other HP aircraft speeding up a valley or box canyon where the end is not visible from the entrance. They finally get to the end and realize it is not the one they had intended on using. Higher speeds require a greater turning radius, and often the distance available is not sufficient.
Monarch Pass (Denver Sectional, 38.30.00N 106.20.00W), just West of KANK, is one of the more treacherous in Colorado, and has had over a half dozen wrecks right on the ski area sitting at the summit. With the pass road at 11,312', the peaks right next to the road go up to 12,867'. I have been through this pass as low as 12,500', but prefer to be at 13,000'. The winds from the West really howl through this particular pass.
The AWOS-3 sitting right on the peak reports altimeter settings of 30.60 and above quite regularly. A calm day is anything under 15kts, but they often reach 60 kts or better. And the OAT can be almost anything from -15C to 25C.
Combinations of the wind and density altitude have created many problems for pilots trying to get through here. They will often try to stay to the right side of the valley as it turns southward, and the falling air just pushes them downward. By the time they manage to stabilize their aircraft, they have lost precious altitude. At that point, the valley also narrows considerably for the last mile or so, just before the pass itself. This further limits the ability of the aircraft to make a successful turn back down valley. The road is too winding to even think of an attempt to land on it, so the option is to put it down where its open, somewhat flat, and has people within a very short distance.
Most seem to make a semi-controlled crash on the lower half of the ski area, but a few have tried to make it over and CFIT on the higher slopes. We will never know how many have actually been successful in getting over the pass after having first gotten into trouble. But the number of those who didn't seems to grow every couple of years.
Tincup (12,154') and Cottonwood (12,126') Passes are the two passes immediately to the North of Monarch. Several aircraft have mistaken them for Monarch, and gotten caught trying to reverse course. If you do make it over either of them, you are in for a big suprise! Big in the form of ranges and peaks in the mid-13's and up into the 14's! There is a narrow valley which heads toward Aspen (ASE), but you are not out of the mtns yet! You must follow that narrow valley NW which brings you in right over the town of Aspen. Your average altitude is still going to be above 11,000'. And trust me- there will be a lot of very close rock much higher than you are. Expect moderate turbulence in this valley, as it is a major wind tunnel!
