How high above sea level is Colorado again? Amazing they can still play competitive sports at that altitude.
There was a controversy a while ago where FIFA tried to restrict international games being played at high altitude. Looking it up, the resolution was that players needed to arrive in the city at least one week prior to the match if the altitude was 2,500 to 3,000 meters, and two weeks prior if it was above 3,000 meters. It proved unpopular and they eventually rescinded it though.