Well, as I understand it, the ozone layer is the layer which controls how much ultraviolet light gets to the surface of the Earth. It is located between 7 - 30 miles above the ground. Significant changes in the concentration of this UV-blocking molecule only happen at altitudes above about 20,000 feet or so. This means that below this altitude, it probably doesn't matter if you are at sea level, or at 10,000 feet which is the altitude of some of the tallest mountain ranges in the continental United States. The amount of UV you get, which gives you sun burns, is probably pretty constant up to 10,000 feet, and probably doesn't change appreciably unless you got above 30,000 feet where most commercial jet planes fly.