Geologic History of Denali National Park

Denali national Park lies in the heart of a curved mountain chain about 600 miles long, the Alaska Range. In the McKinley massif area, the range is about six miles wide and is aligned generally northeast to southwest. This is the highest part of the range with many peaks over 10,000 feet high. Elsewhere in the range, the mountains are mostly between 7000 to 9000 feet high.

The centerpiece of these high mountains is Denali, the highest peak in North America, at 20,320 feet. "Denali" means "the high one" in a local Athabascan dialect. Officially the mountain is still called Mt. McKinley and visitors from the lower 48 will know it as McKinley. However, to Alaskans the mountain is 'Denali'. In terms of vertical relief or elevation from base to summit, Denali is the tallest mountain in the world.

Denali consists primarily of a dome or pluton of granite. About 60 million years ago during the Paleocene epoch, semi-liquid magma intruded into the crust of the earth and slowly cooled underground to form the McKinley pluton. Another pluton formed approximately 38 million years ago and resulted in the formation of Denali's neighboring peaks. As the millennia went by, a sea covered the area where the park is today and deposited much sediment.

Later, a tropical forest covered the area resulting in the coal bearing formation which is mined near the park today. Eventually, geologic forces caused the land to rise and buckle resulting in the metamorphic rock or rock that has been transformed from one type of rock into another by heat or pressure, sequences found in the park today.

Very recently, about 5 million years ago, the Alaska Range began to be uplifted; it is one of the youngest mountain ranges on earth. With the uplift came erosion; the rock layers on top of the McKinley granite pluton were slowly taken away until the granite itself was exposed on the surface. The same is true for Denali's neighbor Mt. Foraker and other high peaks in the Alaska Range. Granite is a very hard, erosion-resistant material. It is also a little less dense than other rocks and therefore a little more buoyant, which is the reason for Denali to be lifted higher than any other mountain in North America.

A major fault, the Denali fault also plays a role in the height of Denali. At the Denali Fault, lateral and vertical offset movement continues to occur as evidenced by many earthquakes in the region. The rocks on the south side of the fault have been raised many thousands of feet. The steep north face of Denali, known as the Wickersham Wall, rises 15,000 feet from its base, and is a result of this relatively recent movement. Also, the southern part of the plate slides to the west, the northern part to the east. Interestingly enough, when Denali first started to be uplifted it was located 200 miles to the east of its current location. In a few million years, these two parts of the plates slid 200 miles by each other.

The highest and most rugged peaks in Denali national Park, such as Denali, Mount Foraker, and Mount Hunter are carved from granite rocks. On the southeast side of Denali in the Sheldon Amphitheater and Great Gorge area enclosing the upper part of Ruth Glacier, great spires and walls of granite soar thousands of feet above the ice. The granite Cathedral Spires at the southwest end of the park in the Kichatna Mountains are the highest strand of vertical rock in North America.