Denali National Park is located in central Alaska and covers an area of 6 million acres. The park is known for its astonishing mountains, the tallest being Mount McKinley, which is also the tallest mountain in North America. It peaks in at an elevation of over 20,000 feet, almost 4 miles above sea level. The lowest elevation in the park is located at the Yentna River. This National Park, located at the center of the Alaskan Range, sees on average a 70°F high and a -9°F low every year. The Park has a wide variety of different types of ecosystems and biological communities ranging from high, mountainous terrains to low land forest and vast stretches of tundra. The winters are often long and the spring and summer seasons are short lived for the most part. The weather in Denali is almost unpredictable, so unpredictable that there have been cases of snow in august. The climate on the North and South sides of the mountains are very different. The Southern side of the mountains often has more moisture than the Northern side because the mountains block the flow of water to a certain degree. The mountains that define the whole park and offer a variety of life, along with the beauty that comes with it, were formed by the collision of tectonic plates. The North American plate and the Pacific Plate have been colliding for millions of years and they have shaped the unique terrain of Denali National Park. Glaciers have also left their mark on the land, making craters and valleys. The Park is made up of many types of rocks, some being as old as 500 million years old. These rocks sometimes contain fossils that are not only important to discovering the history and climates of the Park, but they also provide possibly essential information for understanding the chain of evolution.