Complex sentence: According to the Geographic Names Information System (GNIS), Pinnacle Mountain is a summit, which is defined as "a prominent elevation rising above the surrounding level of the Earth's surface" and does not include mountains, among other things.
Split into simpler sentences: According to the Geographic Names Information System (GNIS), Pinnacle Mountain is a summit. A summit is defined as "a prominent elevation rising above the surrounding level of the Earth's surface" and does not include mountains, among other things.