OH, jeesh, I see you are coming from sea level. Drink at least a gallon of water in the 24 hours before you arrive. And then always have a bottle of water with you and never let yourself get thirsty. Altitude sickness usually doesn't happen below 7000 ft, but Castle Rock is about 6500 and if you head into the mountains at all, it can happen at any time. It's caused by the human body reacting to lack of oxygen by thickening the blood and you fight it by keeping hydrated. It can ruin a vacation.