Nearly three dozen earthquakes have rattled the Mammoth Lakes region in less than 24 hours as the area continues to experience ripple effects of "volcanic unrest," according to the U.S.

The USGS said Friday it is "closely tracking" a swarm of hundreds of earthquakes that began Thursday in an area near the Sierra Nevada resort town of Mammoth Lakes.

Long Valley is situated next to Mammoth Mountain and is one of the world's largest calderas, a huge, cauldron-like hole that forms after an eruption. The caldera at Long Valley is huge, measuring ...