North Cascades National Park was named after the North Cascades mountains, which are a subsection of the Cascade Range that extends from northern California into British Columbia. The North Cascades are the northernmost section of the range and unlike their southern counterparts that consist of Tertiary to Holocene volcanic rocks, the North Cascades are composed primarily of Mesozoic crystalline and metamorphic rocks. Though most rocks in the park are from the more recent Mesozoic, the oldest rocks are 400 million years old, dating from the Devonian. A complex assemblage of various rock formations have repeatedly been eroded, reburied, subjected to fracturing and heat, creating a geological puzzle that is one of the most complicated and least understood geological records in North America. These forces are ongoing and the region continues to see uplift and faulting.