Sierra Nevada in California is home to towering sequoia trees, the oldest and tallest on Earth. Found only in California, some of these "living fossils" are 3,000 years old, with an average height of approximately 300 feet.

Scientists from the University of California, Berkeley conducted a study to see how the severe four-year drought affected the sequoia trees. They climbed up to the trees' green canopies for closer inspection.

The historic California drought has caused these giant sequoias to show signs of stress in the form of increased dead foliage in recent years. The trees bear more rotting patches than normal, with 75 percent of sequoia groves showing worsening conditions.

Biologists said the trees started showing signs of decay during the drought's fourth year, when the hottest temperatures were recorded.

"We've observed some unusual and abnormal levels of foliage die-back, which haven't been observed in the park before," said Anthony Ambrose, one of the biologists involved in the study.

These giant redwoods survived nature's notorious challenges such as droughts, wildfires and weather fluctuations. One sequoia tree needs over 800 gallons of water daily. The once abundant mountain streams provide water to the trees, but with the drought as a threat, the giant redwoods are getting significantly less water.

The scientists are carrying on with their study to measure the severity of the drought's effect on the trees. Through canopy sensors that measure temperature and humidity, aerial images and examination of the trees' seedlings, the scientists are hopeful they can pin down the seriousness of the dangers surrounding the living fossils.

They proposed cutting down lesser species that continue to compete with the redwoods for water supply. A prescribed burn of less significant groves mean there would be less competition for the diminishing underground water. Another proposed solution is to thin out some groves.

"They're beautiful, majestic trees," said Koren Nydick, an ecologist for the National Park Service who assisted the research team.

Locals and tourists from all over the world come to Sierra Nevada to see the giant sequoias. It's the only place on Earth where these living fossils can be found.

Nydick added that there is so much to be done to save these trees from going extinct.