Take an analogy:
A smooth skin covers all underneath parts vs.a cool soil surface of the earth enclose a hot core of magma?
Granite
Terra Sierra: GRANITE: THE STONE HEART OF THE SIERRA
by Frank DeCourten
On a recent trip home from the valley, I was driving east over Donner Summit at sunset when the bright flash and glittering sparkle pierced the corner of my eye. From the low road cut on my left, the reflected sunlight glistened with such brilliance that it seemed somehow electrified. How different, I thought, was this glittering outcrop from the monotonous dull brown exposures of volcanic rocks farther east, or the drab slate gray of the roadside rocks miles behind me. The beauty of the rock reminded me of the words used by John Muir in 1894 in his loving description of the Sierra Nevada as a mountain range:
“ … so luminous, that it seems to be not clothed with light, but wholly composed of it, like the wall of some celestial city.”
Muir’s famous allusion to the Sierra as the “Range of Light” and the burnished outcrops of rock along Donner Summit both signify one of the most fundamental aspects of Sierra Nevada geology: granite. So common is granite in the Sierra Nevada that the range is often described (inaccurately) as a mountain system comprised solely of it. In fact, though granite comprises the foundation of the Sierra Nevada, other types are rocks are equally abundant at the surface, especially in the portion of the range north of Yosemite National Park. Nonetheless, granite, or rock very similar to it, is widely exposed on the surface, and does comprise most of deeply buried and unseen foundation ...
