Yosemite, like most of the Sierra Nevada, was carved from an intrusive igneous rock (subterranean magma that cooled without reaching the surface). This subterranean magma cooled slowly enough for its primary constituents, quartz and feldspar, plus mica and other minerals, to form crystals that fuse into an extremely hard matrix: granite. The granite waited patiently in the dark while overhead oceans advanced and receded, leaving thousands of feet of new sediment behind.
Beginning tens of millions of years ago, a slow-motion collision of tectonic plates uplifted the granite and its overlying sedimentary layers. As the ancient mountain range rose, erosion accelerated the demise of the sedimentary layers, eventually exposing the much harder granite. As the uplift continued, rivers moved faster, carving V-shaped river valleys that included the predecessor of what we now know as Yosemite Valley.
Then came the glaciers, an irresistible force meeting granite’s immovable object. Instead of breaking apart and collapsing as a lesser rock might, Yosemite’s granite stood tall as the glaciers cleared out the ancient Yosemite Valley, carving it into the U-shaped feature we know today—a flat floor bounded by vertical cliffs.
Granite’s hardness also affects the way it breaks up when exposed to the elements of weathering. Instead of crumbling under wind and rain like softer rock, or cleaving along aligned planes of weakness, granite retains its shape until fracturing along microscopic cracks caused by external stress such as pressure or weathering. These cracks allow water to seep into the rock. Of course you remember from high school science (right?) that unlike most substances, water expands when it freezes. This expansion pushes open the cracks, allowing even more water to seep in after the ice melts. This crack/seep/freeze/expand cycle continues until the rock fails, splitting along the expanded crack. In this process large chunks of granite are shed, often quite suddenly, while the remaining granite stands tall.
Granite’s unique qualities are on exquisite display in Yosemite Valley, where streams bursting with snowmelt tumble over shear granite walls, and granite monoliths tower 3,000 feet above the Merced River. Yosemite and Bridalveil Falls are Yosemite’s most recognized waterfalls, but look up on a spring day and you might count a dozen or more. The waterfalls dominate in spring, but Yosemite’s monoliths endure year-round, drawing visitors from around the world in every season. El Capitan, the largest chunk of granite in the world, is a climbers’ mecca, and few mountains have a more recognizable profile than Half Dome.
Half Dome is a bit of a misnomer, but one look at it the name is easy to visualize a rounded dome that lost a full half of its mass to a passing glacier. The reality is that Half Dome’s current shape is fairly close to the rock that was exposed by millions of years of erosion. While Yosemite’s glaciers filled most of Yosemite Valley, Half Dome was tall enough to protrude from the ice sheet and avoid direct contact. Half Dome’s shear face resulted from a single fracture that separated a large slice of granite to expose the flat granite face we all recognize.
After a nice day photographing fall color and reflections El Capitan’s shadow, we finished our day at Glacier Point for a face-to-face view Half Dome. The gray stratus blanket that had permitted a full day of sweet photography in diffuse the sunlight was about to become a liability for anyone longing for a colorful sunset.
Half Dome gets light all the way up to, and in fact even a couple of minutes beyond, the “official” (flat horizon) sunset. But because the view of Half Dome faces east, and the view to the west is obscured by terrain, there’s no way to know whether the horizon is clear in the direction of the setting sun. Even on cloudy days like this, my rule in Yosemite is to never give up on sunset until at least five minutes the after the official sunset time has passed. When a couple of people in the group started rumbling about heading back to the cars, I issued one of my favorite Yosemite proclamations to all within earshot: Never try to predict the conditions in five minutes based on the conditions now. I knew the odds were long for capturing anything more than darkening shades of gray fading to black, but without cameras they’d be zero.
I have no idea whether they truly believed me, or simply stayed put to humor me, but either way, I started to look pretty smart about five minutes before sunset when we spotted a faint glow on Half Dome. I held my breath as the sun slipped into a clear slot of unknown size on the horizon behind us to paint Half Dome with warm light. I hadn’t planned to shoot that evening, but as the light intensified I was glad I’d dragged my bag around anyway. As I quickly set up my tripod and extracted my camera, I urged everyone to keep shooting because there was no guarantee that this would last—just as I’ve witnessed many of these last minute miracles in Yosemite, I’ve also seen euphoria dashed in a heartbeat when the sun was suddenly snuffed right at the climactic moment (Horsetail Fall is notorious for this). But this evening the light held strong, warming to a golden crescendo, then fading to pink that intensified to a rich red that colored the sky from horizon to horizon.
The light tones of quartz and feldspar, plus its crystalline nature, make granite especially reflective. So while Yosemite isn’t especially known for its sunsets, when they do get red like this, granite’s inherent reflectivity causes the entire landscape to throb with a crimson glow. It’s one of my favorite phenomena in nature.
I ended up photographing the entire sunset with my Sony 100-400 GM lens on my Sony a7RIII. Not because I didn’t have a wealth of wide angle shots to choose from (I did!), but because I was working with my group and the telephoto compositions were simpler. Simpler in the sense that (for me at least) a wide shot requires a bit more strategic planning to first identify the frame’s foreground, middle-ground, and background elements, then position myself to give them a coherent relationship. A telephoto composition, on the other hand, has always felt more intuitive than strategic (though each generally requires elements of strategy and intuition), so I’m usually able to put my camera and telephoto to my eye, then move and zoom until something feels right.
With so many views at Glacier Point, the group had scattered a little before sunset, so I was only with about half of them for the good stuff at the end. Back at the cars I checked in with those who had gone elsewhere and found that while most had photographed it, a couple had watched the show from the parking lot. Sigh.
Very nice photo of Half Dome from Glacier Point, Gary. On a side note I think I’ve read that the structures built in Yosemite Valley could not use “Yosemite” granite and that a lot of it came from near Stone Mountain, near where I live in Georgia.
Thanks, Kent. That’s entirely possible, since Yosemite is a National Park and would almost certainly not allow commercial use of its resources. Park visitors can’t even pick up a rock or pine cone as a souvenir.
What an amazing sunset! Beautiful photos!