The southwestern United States, which is generally dry, had heavy rainfall on Sunday as Tropical Storm Hilary sped across the border from Mexico. Hilary also brought warnings of possibly life-threatening floods.

An earthquake of 5.1 magnitude that occurred close to the southern California town of Ojai put many on edge, although there were no immediate reports of injuries or property damage. 

The US National Hurricane Center (NHC) reported that as of Sunday afternoon, Hilary's core was in California with maximum sustained winds of 60 miles per hour (95 kilometers per hour) after tearing up Mexico's Baja California Peninsula.

This tropical weather event was unusual for southern California, as the storm was traveling quickly -- 23 mph (37 kph). The NHC issued a warning about "potentially historic" rainfall on Sunday night, saying it may "cause life-threatening to locally catastrophic flash, urban, and arroyo flooding" in some areas of the state through early Monday.

A local ABC network showed footage of severe flooding in sections of Palm Springs, which is outside of Los Angeles, and the National Park Service declared Death Valley National Park closed because of "hazardous flood conditions." 

Beach closure orders caused a rush of people to stores to buy water and other necessities. There were warnings for flash floods and even tornadoes in some locations.

Hilary had previously reached Category 4, the second-strongest rating on the five-step Saffir-Simpson hurricane scale, but when it approached the heavily populated Mexican border city of Tijuana, it was downgraded to a tropical storm.

Deanne Criswell, administrator of the US Federal Emergency Management Agency (FEMA), warned citizens to take the threats seriously.

"Hurricane Hilary is going to be a serious impact and threat to southern California," she said on CNN.

According to Newsom's office, authorities opened five storm shelters and sent out more than 7,500 people, including several hundred National Guard soldiers and swift water rescue teams. Sandbags were filled in San Diego to prepare for potential floods, and lifeguards issued warnings for people to keep out of the water. 

'Make no mistake'

Mexico's Civil Protection office reported one fatality after a vehicle was swept away by a flooded river and issued a warning for landslides and road closures in Baja California. 1,725 persons who were impacted by the storm found refuge in 35 shelters that the Mexican army opened. According to the NHC, there might be flash flooding and heavy rain in some areas of Oregon and Idaho.

It stated that there was a chance of tornadoes in southeast California, western Arizona, southern Nevada, and far southwest Utah. This could be one of the worst storms to hit California in more than ten years, according to Nancy Ward, director of the Governor's Office of Emergency Services. She said at a press conference on Saturday, "Make no mistake."

"This is a very, very dangerous and significant storm." Major League Baseball and Major League Soccer replanned the games scheduled for Sunday in the US region.

The federal power service sent 800 employees and hundreds of trucks to deal with any disruptions, and the Mexican government stationed nearly 19,000 soldiers in the storm's hardest-hit regions.

Every year, hurricanes strike Mexico's Pacific and Atlantic shores. California is occasionally affected by storms, but they rarely have a significant impact on the state. Storms are getting stronger as the planet warms due to climate change, according to scientists.

"We have to also look at what is the change in the climate doing to these severe weather events," Criswell, the FEMA administrator, told CNN Sunday. "What is the risk going to look like into the future?"