Every year, once the snow melts, "Dr. V" and his students trek 10,000 feet in elevation, a 10 or 15-mile hike, in search of frogs -- frogs that are mysteriously dying off, creating the beginning of the sixth mass extinction of life on earth in its 4.2 billion years of existence.

A mass extinction is an abrupt decrease in the number of species in a relatively short period of time. The "big five" mass extinctions, from earliest to most recent, are Ordovician-Silurian, Late Devonian, Permian-Triassic, End Triassic and Cretaceous-Tertiary.

"Amphibians are long-term survivors; they've been alive for over 300 million years, but over the last couple of decades, they're dying off," Vance Vredenburg, 40, head of the amphibian research group at SF State and assistant professor of Biology, said." Amphibians in the world are declining and are threatened more than any other group of vertebrates in the world."

Vredenburg, who holds a doctorate in biology, has received a grant of $400,000 from the National Science Foundation to find out what is happening to these amphibians.

Currently, there are about 6,500 known species of amphibians. Within the last decade, 30 percent of them have been threatened with extinction.

"Here in our time, we're watching these extinctions happen," Vredenburg said. "I care. I really care about these species and I think they're really beautiful animals, and I want them around when my children grow up."

Frogs are a part of the earth's natural biological diversity and they're an important player in food webs, by eating millions of tons of insects every day -- many of which carry diseases, like malaria.

"Nobody knows what's going to happen when we delete these big consumers of insects. I don't want to be around to test it," Vredenburg said.

"The unique thing about this disease is that it's coming into protected areas. When you first start looking into this topic, you think there's one question but it's a complicated issue and there's lots of layers involved," Tina Cheng, 28, a graduate student in biology who helps with the research, said. "It's kind of sad that we're going back and trying to put pieces together -- it's beyond recovery."

Research has found that chytrids, an obscure species of fungus living in the water, are what is causing this amphibian annihilation. One group of chytrids is now suddenly attacking amphibians, when none were problematic before. Although the fungus is world-wide, the disease cropped up in 1998, making it relatively new to science.

The disease is called Chytridiomycosis and is caused by the aquatic chytrid fungal pathogen Batrachochytrium dendrobatidis (Bd). This disease causes the frog's skin to thicken, sometimes up to 40 times thicker than normal, and eventually leads to death since many species use their skin to breathe.

Vredenburg's lab is studying the ecology of the disease and why it emerges only in certain areas. They also want to learn why some amphibians survive when infected and others don't. Things they consider are differences in immune response, environment, individual species, and the strains of the fungus.

At King's Canyon, about five hours from San Francisco, the group does 95 percent of their field work research. The group marks the animals, recaptures them, recounts the population and lets them go. They use non-destructive skin swabs to compare the amount of Bd DNA in the sample to a universal set of standards, to see if the fungus is present or not.

Two specific species of frogs that the lab is studying are the Sierra Nevada Yellow-legged frog and the Southern Mountain Yellow-legged frog.

"I am most interested in the ways humans are affecting animals, even in our pristine national parks, and what we can do to be better for the environment and for ourselves as citizens of the Earth," Natalie Reeder, 26, a graduate student in Ecology.

"If frogs go extinct I will be deeply saddened. Although it's difficult to identify a practical reason why, the loss of these animals would be devastating. The loss of any animal species due to human activity is troubling, since it belies our anthropocentric approach to life and our inability to acknowledge the worth of other species on Earth that intrinsically are equally as valuable as our own," Reeder said.

Human activity may be playing a role in the possible extinction. It's possible that humans introduced the disease to new areas around the world by transporting frogs from Africa, Asia and the East Coast. The fungus is causing the disease that is killing these frogs.

Humans have also damaged the environment with pesticides, chemicals and car pollution and that may have compromised the frogs' immune systems to the point where they can no longer fight off the fungus.

"We certainly don't have proof yet of these human causes, but we do know for sure that Sequoia and Kings Canyon National Parks have some of the worst air quality of anywhere in the U.S.," Reeder said. "Although the land itself is protected, the air flows into the parks after passing over the Central Valley. The incredible amounts of chemicals that are used in farming in the Central Valley find their way into the national parks in huge amounts."