thousand feet brings you into the snowbelt, the mixed conifer zone, with snow cover generally from mid-November through March or April. Continued ascent into the montane, subalpine, and alpine reaches of the park, including passage along Tioga Road (CA 120) to Tuolumne Meadows and Tioga Pass, carries you to areas that are inaccessible for 7 months—from the first major snowfall in October or November until at least late May. Spring reaches the low elevations in April and the alpine in June. A warm, mostly dry summer follows. June–August is hot in Yosemite Valley, Wawona, and Hetch Hetchy and pleasant in Tuolumne Meadows and at Tioga Pass. By September, fall, with freezing nights, has arrived at the upper elevations, and within a month the yellow grass and coloring leaves have spread to Yosemite Valley. October brings the first snowfalls at the upper elevations, with snow already sticking in shadowed areas on the higher summits. Soon winter, with snow or persistent rain, has enveloped all of Yosemite. The plants, animals, and most visitors are again waiting for spring.
APPRECIATING THE PARK’S RICH NATURAL HISTORY
Every visitor to Yosemite will absorb some of the park’s wonderful natural history—the granite walls and summits, as well as the multitude of plants and animals, that are experienced every time one steps out of the car and looks around. As you walk, take the time to look around you.
More than 400 species of mammals, birds, and reptiles call Yosemite home. Some of the species are seen by many park visitors: the ubiquitous California ground squirrels around Yosemite Valley and Glacier Point, inevitably begging for food; mule deer, frequently seen grazing in Yosemite Valley and Tuolumne Meadows; blue-and-black Steller’s jays squawking as they fly from tree to tree; chipmunks and golden-mantled ground squirrels scurrying through the upper elevation forests; American black bears trotting confidently through the campgrounds at dusk, waiting for a camper to leave food unattended; marmots sunning themselves on high-elevation boulders; and many more.
Persistent searching—and a dose of luck—might lead to some treats: a weasel peering over a rock, a pika chirping from the middle of a high-elevation talus pile (or at Olmsted Point), a glimpse of a mountain lion in Yosemite Valley, or even a herd of Sierra bighorn sheep near Mono Pass. Other mammal species are so rare that they will likely go undetected during a lifetime of exploring the park. The Sierra Nevada red fox and the fisher are so rare that scientists generally see them only with motion-sensitive cameras. Animal species even continue to be found in Yosemite. In 2010 a new species, the Yosemite cave pseudoscorpion, was found lurking in granite talus in the park. Each species is found in a specific habitat—a particular elevation, meadows versus forests versus peaks—and only by hiking in many of Yosemite’s habitats will a visitor have the opportunity to meet many of the park’s permanent inhabitants.
In addition, 1,350 species of plants, from the giant stately sequoias to minute alpine cushion plants, have been recorded in Yosemite. Each species has its preferred habitat, delineated foremost by elevation (and therefore temperature) but also by moisture, soil depth, rock type, sunlight, and many more factors that create nearly infinite fine-scale habitats across a short distance—you will cross many on even a short walk.
In turn, plants inhabiting each so-called niche look different. At high elevations, savage winds and the heavy burden of a snowpack necessitate a short stature, while in a dense forest, being the tallest herb is advantageous because its leaves intercept the most sun. Plants in drier environments tend to have smaller leaves than those of their streamside compatriots. Meanwhile flowers come in all manner of shapes and colors, each long selected to maximize visitation by certain pollinators. A long tubular red flower attracts hummingbirds, while a wider, shorter, blue-tubed species will be visited by bees. Patchy, yet regular, wildfires are essential to create some habitats and therefore increase the diversity of species that exist in Yosemite. Some wildflowers and shrubs germinate only after an intense wildfire has cleared the overstory, while others thrive beneath a dark canopy of mature pines and even acquire energy directly from the trees’ roots.
Although you may not be able to greet many plants by name, take the time to stare at the myriad of shapes and sizes, considering that no one species can live everywhere but that together plants do a remarkable job of exploiting every inhabitable inch of Yosemite. And of practical importance, two of the most colorful locations are meadows (especially those around 8,000 feet and in the alpine) and along stream banks.
The complex landscape of peaks, meadows, lakes, streams, and cliffs is the backdrop, the milieu that allows Yosemite’s great biological diversity to exist. The geography owes its existence to the many different geologic processes that occurred over the last 100 million years. Here I introduce just three landmark geologic events and intertwined processes. The first is the creation of a vast block of granite, termed the Sierra Nevada batholith, between 105 and 85 million years ago. It formed deep underground as the Pacific and North American tectonic plates collided, forcing the west-lying Pacific Plate deep into the earth. The plate melted, and some of the resultant magma erupted to form massive volcanoes, while the rest solidified underground to form the Sierra Nevada batholith. Today the volcanic rock has eroded and disappeared, while the granite is at the surface. The batholith is composed of many different variants of granite, each comprising its own distinctive combination of minerals and termed a pluton. Extensive planes of weakness exist within the rock, dating from its formation, and once the rock emerges on the Earth’s surface, these weaknesses reveal themselves in several ways. First is exfoliation, whereby curved slabs of rock detach from the surface like the layers of an onion. Sentinel Dome and roadcuts along Tioga Road between Yosemite Creek and May Lake are excellent places to see this. Second are vast fractures that extend across the landscape, likely responsible for the general orientation of Yosemite Valley and many of its vertical walls, including the face of Half Dome.
The second set of geologic events includes various forces that caused the uplift of the Yosemite-area mountains and the surrounding Sierra Nevada. The timing and importance of different episodes of uplift are still uncertain, but geologists have established that a tall mountain range has existed in this location since the formation of the granitic batholith. The major river drainages and layout of the mountains have existed since this time. A more recent uplift event, beginning approximately 10 million years ago, led to a steepening of the mountain range. Hand in hand with uplift, and accentuated when uplift is greatest, is erosion, a slow but continuous process that breaks apart and moves rock from the highest summits toward sea level. Erosion occurs as water and ice flow over the rocks; as the rocks freeze and thaw each year, fracturing them; as animals (and now people) dislodge rocks; and in many other ways. Erosion is what has etched the major river valleys and shaped the peaks.
Third are repeated glaciations beginning just 2 million years ago. The glaciers scoured the landscape, scraping loose rock from the sides of valleys, shaping domes and summits, and polishing the rock. Glaciers did not create Yosemite Valley, but they steepened and smoothed its walls and scoured its base. In Tuolumne Meadows, all but the highest summits were submerged in the ice field, and today visitors can still feel the polished rock, visit endless beautiful lakes, and gaze at the pinnacled summits of the Cathedral Range—all the result of glacial action.
YOSEMITE’S HUMAN HISTORY
California Miwok Native Americans had inhabited Yosemite Valley for many centuries, probably millennia, before a party of explorers headed by Joseph Walker first looked down upon it in 1833. During the subsequent two decades, tensions between the European settlers and Native Americans in the Sierra Nevada foothills increased, leading to an offensive by the Mariposa Battalion in 1851. In search of the Ahwahneechee, the band of Miwok living in Yosemite Valley, these soldiers became the first Europeans to enter Yosemite Valley. This encounter ended badly for the Miwok, who were driven from their home. Just 4 years later the first tourist party reached the valley, and their drawings of Yosemite’s waterfalls and vertical walls soon captivated the world. Yosemite quickly became another opportunity to earn easy money in the undeveloped West, as early settlers set up hotels and toll roads to extract money from the visitors streaming in.
Fortunately a few early visitors already
