Yosemite National Park (California, USA)
Yosemite National Park
Yosemite is one of the largest and least fragmented habitat blocks in the Sierra Nevada, and the park supports a diversity of plants and animals. The park has an elevation range from 2,000 to 13,114 feet (600 to 4,000 m) and contains five major vegetation zones: chaparral/oak woodland, lower montane, upper montane, subalpine, and alpine. Of California’s 7,000 plant species, about 50% occur in the Sierra Nevada and more than 20% within Yosemite. There is suitable habitat or documentation for more than 160 rare plants in the park, with rare local geologic formations and unique soils characterizing the restricted ranges many of these plants occupy.
The geology of the Yosemite area is characterized by granitic rocks and remnants of older rock. About 10 million years ago, the Sierra Nevada was uplifted and then tilted to form its relatively gentle western slopes and the more dramatic eastern slopes. The uplift increased the steepness of stream and river beds, resulting in formation of deep, narrow canyons. About 1 million years ago, snow and ice accumulated, forming glaciers at the higher alpine meadows that moved down the river valleys. Ice thickness in Yosemite Valley may have reached 4,000 feet (1200 m) during the early glacial episode. The downslope movement of the ice masses cut and sculpted the U-shaped valley that attracts so many visitors to its scenic vistas today.
Yosemite National Park is located in the central Sierra Nevada of California. It takes approximately 3.5 hours to drive to the park from San Francisco, approximately 6 hours from Los Angeles, and 7 hours from San Bernardino. Yosemite is surrounded by wilderness areas: the Ansel Adams Wilderness to the southeast, the Hoover Wilderness to the northeast, and the Emigrant Wilderness to the north.
The 1,189 sq mi (3,081 km²) park is roughly the size of Rhode Island and contains thousands of lakes and ponds, 1,600 miles (2,600 km) of streams, 800 miles (1300 km) of hiking trails, and 350 miles (560 km) of roads. Two federally designated Wild and Scenic Rivers, the Merced and the Tuolumne, begin within Yosemite’s borders and flow westward through the Sierra foothills, into the Central Valley of California. Annual park visitation exceeds 3.5 million, with most visitor use concentrated in the seven square mile (18 km²) area of Yosemite Valley.
Almost all of the landforms in the Yosemite area are cut from the granitic rock of the Sierra Nevada Batholith. About 5% of the park (mostly in its eastern margin near Mount Dana) are from metamorphosed volcanic and sedimentary rocks. These rocks are called roof pendants because they were once the roof of the underlying granitic rock.
Erosion acting upon different types of uplift-created joint and fracture systems is responsible for creating the valleys, canyons, domes, and other features we see today. These joints and fracture systems do not move, and are therefore not faults. Spacing between joints is controlled by the amount of silica in the granite and granodiorite rocks; more silica tends to create a more resistant rock, resulting in larger spaces between joints and fractures.
Natural pillars and columns, such as Washington Column and Lost Arrow, are created by cross joints. Erosion acting on master joints is responsible for creating valleys and later canyons. The single most erosive force over the last few million years has been large alpine glaciers, which have turned the previously V-shaped river-cut valleys into U-shaped glacial-cut canyons (such as Yosemite Valley and Hetch Hetchy Valley). Exfoliation (caused by the tendency of crystals in plutonic rocks to expand at the surface) acting on granitic rock with widely spaced joints is responsible for creating domes such as Half Dome and North Dome.
Yosemite Valley represents only one percent of the park area, but this is where most visitors arrive and stay. El Capitan, a prominent granite cliff that looms over the valley, is one of the most popular rock climbing destinations in the world because of its diverse range of climbing routes in addition to its year-round accessibility. Granite domes such as Sentinel Rock and Half Dome rise 3,000 feet and 4,800 feet (900 and 1,450 m), respectively, above the valley floor.
The high country of Yosemite contains beautiful areas such as Tuolumne Meadows, Dana Meadows, the Clark Range, the Cathedral Range, and the Kuna Crest. The Sierra crest and the Pacific Crest Trail run through Yosemite, with peaks of red metamorphic rock, such as Mount Dana and Mount Gibbs, and granite peaks, such as Mount Conness. Mount Lyell is the highest point in the park reaching 3997 meters above sea level.
The park has three groves of ancient Giant Sequoia trees; the Mariposa Grove (200 trees), the Tuolumne Grove (25 trees), and the Merced Grove (20 trees). Giant Sequoias are the world’s largest and among the tallest and most long-living trees — growing trees appeared in the park even before the last glacier period (Geology of U.S. Parklands, page 227).
In a relatively small area of the park there are a big number of waterfalls, among which it is worthwhile to mention the following:
• Bridalveil Fall – 189 m (620 ft)
• Chilnualna Falls – 210 m (690 ft)
• Illilouette Fall – 110 m (370 ft)
• Lehamite Fall – 360 m (1,181 ft)
• Nevada Fall – 181 m (594 ft)
• Ribbon Fall – 491 m (1,612 ft)
• Royal Arch Cascade – 370 m (1,214 ft)
• Sentinel Fall – 585 m (1,919 ft)
• Silver Strand Falls – 175 m (574 ft)
• Snow Creek – 652 m (2,140 ft)
• Staircase – 310 m (1,020 ft)
• Tueeulala Falls – 260 m (840 ft)
• Vernal Fall – 97 m (317 ft)
• Wapama Falls – 520 m (1,700 ft)
• Waterwheel Falls – 91 m (300 ft)
• Wildcat Falls – 190 m (630 ft)
• Yosemite Falls – 739 m (2,425 ft)
Tuolumne and Merced River systems originate along the crest of the Sierra Nevada in the park and have carved river canyons 3,000 to 4,000 feet (900 to 1,200 m) deep. The Tuolumne River drains the entire northern portion of the park, an area of approximately 680 square miles (1,760 km²). The Merced River begins in the park’s southern peaks, primarily the Cathedral and Clark Ranges, and drains an area of approximately 511 square miles (1,320 km²).
Hydrologic processes, including glaciation, flooding, and fluvial geomorphic response, have been fundamental in creating landforms in the park. Apart from two main rivers, there are 3,200 lakes in the park with a gross area over 100 sq. m. each, two water reservoirs and about 2,700 kilometers of different rivers and creeks that belong to one of the two watersheds. Wetlands in Yosemite occur in valley bottoms throughout the park, and are often hydrologically linked to nearby lakes and rivers through seasonal flooding and groundwater movement. Meadow habitats, distributed at elevations from 3,000 to 11,000 feet (900 to 3,500 m) in the park, are generally wetlands, as are the riparian habitats found on the banks of Yosemite’s numerous streams and rivers.
Numerous sheer drops, glacial steps and hanging valleys (that is, side valleys with floors above the floor of the main valley) in the park provide many places for waterfalls to exist, especially during April, May, and June (the snowmelt season). Located in Yosemite Valley, the 2,425-foot-high (739 m) Yosemite Falls is the highest in North America and third highest in the world. Also in the valley is the much lower volume Ribbon Falls, which has the highest single vertical drop, 1,612 feet (492 m). Perhaps the most prominent of the Yosemite waterfalls is Bridalveil Fall, which is well seen from a nearby road.
All glaciers in the park are relatively small glaciers that occupy areas that are in almost permanent shade, such as north- and northeast-facing cirques. Lyell Glacier is the largest glacier in the Sierra Nevada (and therefore the park) and covers 160 acres (65 ha). None of the Yosemite glaciers are a remnant of the much, much larger Ice Age alpine glaciers responsible for sculpting the Yosemite landscape. Instead, they were formed during one of the neoglacial episodes that have occurred since the thawing of the Ice Age (such as the Little Ice Age in XIV-XVII centuries). Global warming has reduced the number and size of glaciers around the world. Many Yosemite glaciers, which were discovered by John Muir in 1871, have disappeared and most of the others have lost up to 75% of their surface area. (Geology of U.S. Parklands, page 228)
Yosemite has a Mediterranean climate, meaning most precipitation falls during the mild winter, and the other seasons are nearly dry (less than 3% of precipitation falls during the long, hot summers). Due to orographic lift, precipitation increases with elevation up to 8,000 feet (2,400 m) where it slowly decreases to the crest. Precipitation amounts vary from 36 inches (915 mm) at 4,000 feet (1,200 m) elevation to 50 inches (1,200 mm) at 8,600 feet (2,600 m). Snow does not typically persist on the ground until November in the high country. It accumulates all winter and into March or early April.
Temperature decreases with increasing elevation. Temperature extremes are moderated by the fact that Yosemite is only about 100 miles (160 km) from the Pacific Ocean. An anticyclone sits off the coast of California in the summer, sending cool air masses toward the Sierra Nevada that result in clean dry air in the Yosemite area.
Mean daily temperatures range from 25 to 53 °F (-3.9 to 11.5 °C) at Tuolumne Meadows at 8,600 feet (2,600 m). At the southern entrance to the park (elevation 5,130 feet; 1,564 m), mean daily temperature ranges from 36 to 67 °F (2.2 to 19.4 °C). At the lower elevations below 5,000 feet (1525 m), temperatures are hotter; the mean daily high temperature at Yosemite Valley (elevation 3,966 feet; 1,209 m) varies from 46 to 90 °F (7.8 to 32.2 °C). At elevations above 8,000 feet (2,440 m), the hot, dry summer temperatures are moderated by frequent summer thunderstorms, along with snow that can persist into July. The combination of dry vegetation, low relative humidity, and thunderstorms results in frequent lightning-caused fires as well.
Even up to now historians are arguing about who was the first European to see the Yosemite Valley. A group of trappers led by mountain man Joseph Reddeford Walker may have seen Yosemite Valley in the autumn of 1833. Walker approached a valley rim as he led his party across the Sierra Nevada, but he did not enter it. A member of the group, Zenas Leonard, wrote in his journal that streams from the valley rim dropped “from one lofty precipice to another, until they are exhausted in rain below. Some of these precipices appeared to us to be more than a mile high.” The Walker party probably visited either the Tuolumne or Merced Groves of Giant Sequoia, becoming the first non-indigenous people to see the giant trees.
The part of the Sierra Nevada where the park is located was long considered to be a physical barrier to European American settlers, traders, trappers, and travelers. That situation changed in 1848 after gold was discovered in the foothills west of the range. Travel and trade activity dramatically increased in the area during the ensuing California Gold Rush. Resources depended upon by local Native Americans were depleted or destroyed. The first confirmed sighting of Yosemite Valley by a non-indigenous person occurred on October 18, 1849 by William P. Abrams and a companion. Abrams accurately described some landmarks, but it is uncertain whether he or his companion actually entered the valley. But it is beyond doubt that in 1850, Joseph Screech became the first confirmed non-indigenous person to enter Hetch Hetchy Valley and even to settle in it.
The surveying crew of Allexey W. Von Schmidt conducted the first intentional and systematic exploration of any part of the Yosemite area backcountry in 1855 under the auspices of the state program «Public Land Survey System».
Sierra Miwok and Paiute Native American tribes lived on this territory before it was settled by Europeans. When the first settlers arrived here, Yosemite Valley was populated by a group of Native Americans who called themselves Ahwahnechee.
The California Gold Rush in the mid-19th century dramatically increased white travel in the area, which resulted in armed conflicts with the local tribes. To put an end to the continuous skirmishes, United States Army Major Jim Savage led the Mariposa Battalion into the west end of Yosemite Valley in 1851 while in pursuit of around 200 Ahwahneechees led by Chief Tenaya. Attached to Savage’s unit was Dr. Lafayette Bunnell, the company physician, who later wrote about his awestruck impressions of the valley in The Discovery of the Yosemite. Bunnell is credited with naming Yosemite Valley from his interviews with Chief Tenaya.
Bunnell wrote that Chief Tenaya was the founder of the Pai-Ute Colony of Ah-wah-nee. The Miwoks (and most white settlers) considered the Ahwahneechee to be especially violent because of their frequent territorial disputes, and the Miwok word “yohhe’meti” literally means “they are killers”. Correspondence and articles written by members of the battalion helped to popularize Yosemite Valley and surrounding area.
Tenaya and the rest of the Ahwahneechee were eventually captured and their village burned; they were removed to a reservation near Fresno, California. Some were later allowed to return to Yosemite Valley, but got in trouble after attacking a group of eight gold miners in the spring of 1852. The band fled eastward to Mono Lake, and took refuge with the nearby Mono tribe, which violated the laws of hospitality and killed them.
In 1855, entrepreneur James Mason Hutchings, artist Thomas Ayres and two others were the first to tour the area. Hutchings wrote articles and books about this and later excursions in the area, and Ayres’ sketches became the first accurate drawings of many prominent features. Photographer Charles Leander Weed took the first photographs of the Valley’s features in 1859. Later photographers included famous Ansel Adams.