Yosemite National Park
Stretching for almost 400 miles near California's eastern border, the Sierra Nevada is a saw-toothed spine of blue-gray ridges and alabaster peaks, the longest and highest unbroken mountain range in the lower 48 states. At its stony heart lies Yosemite National Park, a spectacular showcase where wooded groves boast some of the world's largest trees, pageants of wildflowers strew color over ice-sculpted canyons, alpine gardens nestle at the foot of glaciers, and roaring waterfalls leap from the shoulders of enormous granite cliffs.
Unlike the Rockies and Cascades, the Sierra Nevada is not a chain of individual mountains but a single block of solid granite, ranging from 50 to 80 miles wide. A massive piece of the earth's crust that was thrust upward as a whole and then tilted by powerful geological forces deep within the earth, the Sierra rises more than 14,000 feet from low foothills on the west and culminates in a nearly perpendicular wall on the east. En Masse, the great snow-topped range looks like an immense ocean wave surging mightily toward the east.
As the Sierra gradually tilted upward, the steeper incline turned mountain rivers into torrents that created V-shaped valleys as they sliced downward through the rock. The higher the peaks were thrust, the colder they became. More snow fell in winter than could melt in summer, building up an accumulation thousands of feet deep. Under this pressure, the snow hardened into glacial ice, and when the frozen fingers began creeping downslope, they followed the paths of least resistance: the valleys. The glaciers' great weight dramatically altered the landscape, broadening valleys, shearing mountaintops, and scooping out canyons and basins.
One valley, already impressive from the chiseling force of the Merced River, became grander still. Seven miles long and up to a mile wide, Yosemite Valley is a grassy, tree-dotted stone corridor, dominated from end to end by a commanding procession of granite battlements. Rising more than 4,000 feet, these cliffs have been honed into a variety of mesmerizing shapes: knobs and spires, rounded domes, angular monoliths. Standing out from the rest are two massive and unforgettable rocks. Like sentinels, El Capitan and Half Dome guard both ends of the valley. Throughout the world, their bold, vaulting silhouettes are symbols of this park.
Of the two, El Capitan, its name is Spanish means "The Captain", most crowds the valley floor, its broad shoulders flanking the western gateway. It is the world's largest solid granite rock, and its substance is so strong that its base is nearly free of broken boulders and other rocky debris. With its sleek, nearly vertical profile rising 3,604 feet above the Merced like the prow of an ocean liner above the sea, El Capitan is unquestionably Yosemite's most precipitous rock.
At the opposite end of the valley is Half Dome, its huge, hulking shape looming like a monk's hooded head. Although its northwestern face looks as if a sharp cleaver had cut straight through, the prominent dome has never known a glacier's touch. Even during the fiercest glacial onslaught, when ice nearly filled the valley rim to rim, Half Dome's top 700 feet remained uncovered, like a rocky islet in a frozen sea. But glaciers affected Half Dome's summit nonetheless. As the ice moved down the valley, it undercut the mountain's base, causing the unsupported upper layers to break and fall atop the glacier. The face of the mountain has been sheared ever since.
There are many other domes in the park, Basket Dome, Sentinel Dome, Liberty Cap, Turtleback Dome, Mount Watkins, Mount Starr King. Each is a solid granite block, smoothly rounded like a new helmet and as barren as the Sahara. Contrary to popular belief, glaciers did not rub these enormous blocks into smooth domes. Rather, their roundness is the result of a process called exfoliation, by which granite sheds its outer layers as an onion sheds its skins. As temperatures change, the granite expands and contracts; this causes horizontal cracks to form and layers to develop in the rock. (Some of the granite layers are immense: Half Dome's measure 6 to 10 feet, and Royal Arches' may surpass 100.) Gradually, the granite's top layer rises, breaks apart, and peels off, relieving the pressure on the layer beneath and giving it room to rise. Over the course of eons, after many successive peelings, a dome could smooth itself right out of existence, as some undoubtedly have done. Solid granite is the only type of rock to form domes in this way, and such domes are relatively rare; Yosemite, in fact, has the world's largest collection.