Читать книгу The Pacific Crest Trail. Hiking the PCT from Mexico to Canada онлайн

10 страница из 49

Over the last two million years, major glacial erosion has produced the fantastic rock scenery and the multitude of lakes we see today in the Sierra Nevada. Granite is an ideal rock for the formation of lakes; most of those you will see in Northern California and Oregon are actually on outcrops of granite in a primarily volcanic landscape.

The situation is further complicated by the San Andreas Fault System, which developed about 30 million years ago and resulted in some rocks being transported as much as 200 miles to the north-west. Hot magma is still present near the surface. Evidence appears in the form of hot springs, such as Deep Creek Hot Springs in San Bernardino National Forest, passed on the PCT. Water flowing underground is heated by the hot magma before coming to the surface.

North of Sonora Pass, in Central California, the rocks become predominantly volcanic although there are outcrops of granite and some of metamorphic rock, such as the limestone in Marble Mountain Wilderness. The northern end of the Sierra Nevada is further complicated in that much of it was buried in volcanic ash about 30 million years ago. Then, ten million years ago, massive lava flows caused metamorphosis of existing rocks, after which erosion left a very complicated geological story.