Mendel Glacier is a dirty little chunk of melting ice in an alpine wilderness, yet it became a media star three years ago when a long-dead human body surfaced.

The body belonged to one of four U.S. airmen who died on Mendel in a 1942 plane crash. A second body was found on the glacier in 2007.

In news accounts of the startling discoveries, people around the world may have learned something they did not know about sunny California -- it has glaciers.

Mendel is one among hundreds of small glaciers strewn along the Sierra Nevada crest from Yosemite National Park to Sequoia and Kings Canyon National Parks. They form the southernmost group of glaciers in the United States.

A frigid, alpine wilderness may seem like a freak of nature only 70 miles east of Fresno, where summer temperatures commonly hit triple digits. But Mendel and other glaciers exist because the Sierra soars more than 2 1/2 miles above sea level.

When Pacific storms drop a gentle rain on Fresno, there's often a blizzard at Mendel, with 75 mph winds.

Winter seems forever at 13,000 feet in the Sierra. It is not unusual for nighttime temperatures in May to dip into the teens. In June, snowstorms batter the high Sierra.

Summer season lasts six to eight weeks, and snow on northeast-facing peaks can remain for centuries. Glaciers are an accumulation of such unmelted snowfall, which slowly compresses into ice and begins to move slowly downhill.

The glaciers in the Sierra are tiny and unimpressive compared with glaciers in Washington, Oregon, Colorado, Montana, Wyoming and even Northern California.

The ice in Antarctica, Greenland, Canada and Alaska is downright imposing.

If Greenland's ice melted, the world's oceans would rise 20 feet. Antarctica's ice is more than two miles thick in places. Mendel Glacier is maybe 250 feet thick.

At the same time, there is evidence that the Sierra had its share of big glaciers in the past. In the last 30,000 years, scientists say, there was a 60-mile-long glacier that filled the Grand Canyon of the Tuolumne in Yosemite National Park. Tons of moving ice sculpted breathtaking granite landscapes such as Hetch Hetchy Valley.

Glaciers are slow-motion rivers of ice, battering and crushing whatever is in front of them. Over thousands of years, V-shaped river valleys become U-shaped, with dramatic waterfalls flowing from the vertical walls left behind.

Crevasses, or big trenches, open up as the glacier pulls apart in places. And, as they move, glaciers push up big piles of rock and earth out front and to the sides. They are called moraines.

Mendel is a rock glacier, meaning granite has fallen onto the ice and become part of the flow. The granite gives Mendel advantages that so-called clean glaciers do not have.

"The rock helps to insulate the ice from melting," said glacial geologist Douglas H. Clark of Western Washington University.

Mendel's core of ice could be up to 2,000 years old, he said. Meanwhile, next-door neighbor Mount Darwin has a clean glacier. Clark, who has hiked Mendel and Darwin, said Darwin's ice probably is no more than a few centuries old because it is not as well protected.

Even with its protection, small glaciers like Mendel will disappear in the next several decades because of climate warming, most experts say.

Melting is occurring on top of the glacier, so it grows more shallow each year -- which is perhaps one reason the bodies of the 1942 airmen are emerging from the ice. But even as it melts, Mendel Glacier continues to inch forward.

No one knows how far Mendel Glacier is moving down the mountainside each year, Clark said, but a similar rock glacier nearby is moving about 3 feet annually.

Larger glaciers in places such as Alaska are remnants of the Ice Age that ended 10,000 to 12,000 years ago. That's not true in the Sierra.

Scientists believe Sierra glaciers melted after the last Ice Age and formed again during cooler times. The Sierra's ice returned about 3,200 years ago, said Clark and fellow glacial geologist Niki Bowerman.

They examined sediment cores taken from lake bottoms where glaciers have drained for thousands of years.