arc are over in elevation, and the two highest, Mount Rainier and Mount Shasta, exceed . By volume, the two largest Cascade volcanoes are the broad shields of Medicine Lake Volcano and Newberry Volcano, which are about and respectively. Glacier Peak is the only Cascade volcano that is made exclusively of dacite. The history of the cascade volcanoes can be separated into three major chapters which are discussed below. West Cascades period The time between 37 million and 17 million years ago is known as the West Cascades period, this era is characterized as being when the volcanoes in this region were exceptionally active. During this time the arc was situated a little further west than it is today. One volcano that was active during this time was the Mount Aix Volcanic Complex, which erupted more than 100 km3 (24 mi3) of tephra and pyroclastic debris over the span of just three eruptions. Lavas representing the earliest stage in the development of the Cascade Volcanic Arc mostly crop out south of the North Cascades proper, where uplift of the Cascade Range has been less, and a thicker blanket of Cascade Arc volcanic rocks has been preserved. In the North Cascades, geologists have not yet identified with any certainty any volcanic rocks as old as 35 million years, but remnants of the ancient arc's internal plumbing system persist in the form of plutons, which are the crystallized magma chambers that once fed the early Cascade volcanoes. The greatest mass of exposed Cascade Arc plumbing is the Chilliwack batholith, which makes up much of the northern part of North Cascades National Park and adjacent parts of British Columbia beyond. Individual plutons range in age from about 35 million years old to 2.5 million years old. The older rocks invaded by all this magma were affected by the heat. Around the plutons of the batholith, the older rocks recrystallized. This contact metamorphism produced a fine mesh of interlocking crystals in the old rocks, generally strengthening them and making them more resistant to erosion. Where the recrystallization was intense, the rocks took on a new appearance dark, dense and hard. Many rugged peaks in the North Cascades owe their prominence to this baking. The rocks holding up many such North Cascade giants, as Mount Shuksan, Mount Redoubt, Mount Challenger, and Mount Hozomeen, are all partly recrystallized by plutons of the nearby and underlying Chilliwack