Sierra Nevada: Range of Snow and Ice
Note: This article is taken from material prepared for the 2005 exhibit at the California Academy of Sciences called “Hotspot: California on the Edge.”
The Sierra Nevada, which means “snowy range” in Spanish, stretches 400 miles (644 km) along California’s eastern flank. It is bounded on the west by the Great Central Valley and on the east by the Great Basin. In cross section, the Sierra is shaped like a triangular wedge, with a much steeper slope on the east side than the west.
About 1.8 million years ago, after the Sierra Nevada began to rise, the Earth’s atmosphere turned cold, marking the beginning of the Pleistocene, the last ice age. Glaciers grew high in the mountains and moved slowly down former stream channels, carving U-shaped valleys as they advanced. Small glaciers still exist at the highest elevations in the Sierra Nevada, where they continue to scour the landscape.  The plants and animals that live at high elevations have special adaptations for surviving the cold, harsh environments.
About 1.8 million years ago, the last ice age began. A period of long-term cooling of Earth’s climate resulted in the expansion of continental and polar ice sheets and mountain glaciers.
As much as 30% of all the continents were covered by glaciers and parts of the northern oceans were also frozen.
During this ice age, no massive ice sheets covered California. Glaciers were confined to high mountains, advancing and retreating 4 to 7 times.
The last ice age ended just 10,000 years ago, but several small glaciers still persist in California at high elevations.
A species that lived during the last ice age and still persists today is called a Pleistocene relict. Its present-day distribution is a remnant of its wider range during the last ice age. The grizzly bear and California condor are both Pleistocene relicts – one is extinct in California, the other is barely clinging to existence.
California condor Gymnogyps californianus
They once ranged widely over the dry foothills and mountain ranges of central and southern California where they nested in caves and cliff overhangs.
Destruction of habitat, poaching, and lead poisoning led to the California condor’s decline. By 1985 populations plummeted to fewer than 9 birds in the wild.
At that time, conservation biologists decided to capture the remaining birds to protect and breed them.
Captive breeding programs have released birds back into the wild, but their long-term survival is still in question. Today [2005], 85 of the 222 birds in existence, are in the wild [The population estimate in May 2013 was 198 birds in captivity and 237 in the wild for a total of 435]. The California condor is the largest land bird in North America. An adult can weigh up to 25 pounds (11 kg) and have a wingspan up to 9.5 feet (3 m). Condors can soar for hours at altitudes of 15,000 feet (4572 m), cover hundreds of miles, and reach speeds over 55 mph (89 kph). Like most other vultures, condors eat carrion.
Grizzly bear Ursus arctos californicus
Grizzly bears once roamed the valleys and mountains of California, probably in greater numbers than anywhere else in the continental United States. It was the largest and most powerful mammal in the state.
Fueled by the discovery of gold, California’s population grew rapidly and humans and grizzlies came into contact more frequently.
Less than 75 years after the discovery of gold, every grizzly bear in California was gone. The last wild grizzly was killed in 1922.
The story of “Monarch” Monarch was captured from the wild and died of old age in captivity in 1911. After his death, he was donated to the California Academy of Sciences by the de Young Museum. He remains a legacy to the once mighty California grizzlies.
The California grizzly bear was designated the official state animal in 1953 and appears on the state flag.
Fire Suppression - Restoration of natural fire cycles is important to restoring and protecting biodiversity in the Sierra Nevada. After a fire, the sequence of recovery of native plants provides wildlife with a variety of ecological opportunities.
Global Warming - As concentrations of greenhouse gases in the atmosphere increase temperatures, glaciers are retreating at an accelerated rate. California’s small mountain glaciers are particularly sensitive to warming.
Conservation - In 1913, after a bitter battle, Congress gave San Francisco permission to dam the Tuolumne River at Hetch Hetchy Valley in Yosemite National Park. Following this action, legislation was passed that made it illegal to ever put a dam in any national park again. Studies by the University of California, Davis show it may be possible to restore the valley by impounding Tuolumne River water at existing dams further downstream.