The Mammoth Lakes area in Northern California, part of one of the most active volcanic regions in the state, has been shaken by more than 600 small earthquakes, ranging from magnitude 1.0 to 3.8, in less than 36 hours.

Ripple effects as well continued across one of the most seismically active volcanic regions in California, according to the United States Geological Survey, Reuters reported

The swarm of quakes began just before 5 a.m. Thursday, the USGS said.

"This is one of the largest earthquake swarms we've seen in the past decade or so," David Shelly, a USGS research seismologist who has been studying the volcanic system near Mammoth Lakes, said in the Reuters report. "We'll be tracking it closely."

Residents reported periodic rattles through the day but said they were used to the shaking, since the Mammoth region is typically a seismically active area.

Earthquake swarms are not uncommon to this portion of California's Eastern Sierra Nevada range. Countless small faults crisscross the area known as the Long Valley Caldera, Shelly said.

Roughly 20 miles wide, the crater-like depression next to Mammoth Mountain was formed from ash and pumice deposits during a giant volcanic eruption about 760,000 years ago.

At 11,053 feet, Mammoth Mountain is a lava dome complex on the southwest rim of the caldera and last erupted about 57,000 years ago.

The central part of the caldera has been uplifting slowly in recent decades, and these earthquake swarms happen episodically as part of the volcanic and tectonic interactions in the area, Shelly told Reuters.

Deep below the surface, there is magma, although the magma is not what's moving, Shelly said. The earthquakes are usually triggered when water and carbon dioxide above the magma move up into higher layers of the earth's crust and into the cracks of the small faults. The increase in fluid pressure sets off the movements.

"It doesn't mean that the volcano is any more active," Shelly said. "It's an ongoing process in an volcanic system."

The last large swarm occurred in 1997, when temblors as high as magnitude 4.9 shook the region. Thousands of earthquakes were part of that sequence, which lasted several months, Shelly said.

"At this point, we don't know if it would continue to die down, or if there'd be another stage to this swarm," Shelly said. "This is certainly an interesting scientific opportunity to better understand the processes that are driving this activity."