Well, it's great if you know the geography of the USA well enough to remember that 48 states are called the Mainland of the U.S., but still it's not the whole of the country. The list doesn't include 2 more states so that's why we speak about Mount Whitney but not about Mount McKinley (situated in Alaska).

Whitney's elevation above the sea level is said to be over 14,505 ft and that makes it the highest summit of the ancient mountain range known as Sierra Nevada.