Landscape

Yosemite is best known for the massive granite cliffs and domes found within the park. The landscape began forming about 10 million years ago when 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 one 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 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. The park is also home to the Yosemite Falls, which at 2,425 feet (782 m) is the highest waterfall in North America, and Mount Lyell is its highest point at 13,120 feet (4,000 m) above sea level.

Flora and Fauna

Yosemite has more than 300 species of vertebrate animals, and 85 of these are native mammals. Black bears are abundant in the park, and are often involved in conflicts with humans that result in property damage and, occasionally, injuries to humans. Visitor education and bear management efforts have reduced the bear-human incidents and property damage by 90% in the past few years. There are large numbers of mule deer, as once there was Bighorn sheep, but they have been reduced to only a few remnant introduced populations. There are 17 species of bats, nine of which are either Federal or California Species of Special Concern, and over 150 species of birds. Other species that are found within the park include bobcat, gray fox, mountain beaver, great gray owls, white-headed woodpeckers, spotted owls, golden-mantled ground squirrel, martens, Steller's jays, pika, yellow-bellied marmot, white-tailed hare and coyotes.

The vegetation in the park is primarily coniferous forest, including species of pine, fir, oak and cedar. Most notable among the park's trees are isolated groves of Giant Sequoias, the largest trees in the world, which are found in three groves: the Mariposa Grove (200 trees), the Tuolumne Grove (25 trees), and the Merced Grove (20 trees).

The Wawona Tree, also known as the Tunnel Tree, was a famous giant sequoia that stood in the Mariposa Grove. It was 227 feet (69 m) tall, and was 90 ft (27 m) in circumference. A tunnel was cut through the tree in 1881, which made it a popular tourist photo attraction. Everything from horse-drawn carriages in the late 19th century, to automobiles in the first part of the 20th century, traveled the road which passed through that tree. The Wawona Tree fell in 1969 under a heavy load of snow. It was estimated to have been 2,300 years old!

Climate

Yosemite receives most of its rain in the months of January, February and March and has hot dry Summers. Weather can change rapidly during all seasons of the year, and will also vary greatly with elevation. When visiting it is wise to pack for any season with clothing that can be layered, ready to peel off or add on as conditions dictate. Always include some kind of rain gear as storms are common during the transitional Spring and Fall seasons, with spectacular thunderstorms in Summer and, of course, snow in Winter.

For Yosemite Valley and Wawona (subtract 10-20°F (5-10°C) for Tuolumne Meadows), average weather is as follows:

• Summer Typically dry, with occasional thunderstorms; temperatures from 50°F (10°C) to the low 90°F (30°C) range.
• Fall & Spring Highly variable, with typical high temperatures ranging from 50-80°F (10-27°C) , with lows from 30-40°F (-1 to 4°C). Snow is likely late in Fall/early in Spring.
• Winter Snowy, rainy or (sometimes) even sunny days are possible, with highs ranging from 30-60°F (-1 to 16°C) and lows in the high 20°F (-4 to 0°C) range. This time of the year the roads are less clogged, so if you can handle the cold and have chains for your tires, it can be a great time to visit.