From the World Heritage site:
Yosemite National Park lies in the heart of California. With its ‘hanging’ valleys, many waterfalls, cirque lakes, polished domes, moraines and U-shaped valleys, it provides an excellent overview of all kinds of granite relief fashioned by glaciation. At 600–4,000 m, a great variety of flora and fauna can also be found here.
Yosemite is one of the major parks in the US and one of the first national parks in the US Park Service. The Yosemite valley is one of the most photgraphed and special places in the country. If I had to come up with a short list of places to visit in the United States, this would be near the top of the list.