Firefighters had managed to partially contain a massive wildfire by Tuesday morning after the blaze ignited in a California wildland preserve and spread into Nevada, its smoke blotting out the sun across Las Vegas while flames scorched tens of thousands of acres of desert scrub, juniper and Joshua tree woodland.

The York Fire was mapped at roughly 125 square miles (323.7 square kilometers) on Tuesday, with 23% containment, making it the largest wildfire of the season in California.

The blaze erupted Friday near the remote Caruthers Canyon area of the vast wildland preserve, crossed the state line into Nevada on Sunday and sent smoke further east into the Las Vegas Valley.?

Midday Monday, a smoky haze on the Las Vegas Strip obliterated views of mountains surrounding the city and suburbs. Because of low visibility, the Harry Reid International Airport in Las Vegas reported departure delays of nearly two hours. Firefighters battled “fire whirls” on Monday in their struggle to get the flames under control.

A fire whirl — sometimes called a fire tornado — is a “spinning column of fire” that forms when intense heat and turbulent winds combine, according to the National Park Service.?

The vortexes — which can be anywhere from a few feet tall to several hundred feet high, with varying rotational speeds — were spotted Sunday on the north end of the York Fire. “While these can be fascinating to observe they are a very dangerous natural phenomena that can occur during wildfires,” the park service wrote.

Significant portions of the U.S. population have been subject to extreme heat in recent weeks. Worldwide, July was so steamy that scientists calculate it will be the hottest month ever recorded and likely the warmest to hit human civilization.

Experts say plants like blackbrush scrub, pinyon-juniper woodlands and the famous Joshua trees in the New York Mountains in San Bernardino County are at-risk of taking centuries to regrow naturally, if they are ever able to come back.

The cause of the York Fire remains under investigation, though authorities say it started on private land within the preserve. Other details were not available. To the southwest, the Bonny Fire burned about 3.6 square miles (9.3 square kilometers) in the rugged hills of Riverside County. The blaze was about 30% contained on Monday evening.?

More than 1,300 people were ordered to evacuate their homes Saturday near the community of Aguanga that is home to horse ranches and wineries. However, the fire didn't grow on Monday, and some were allowed back home. One firefighter was injured in the blaze.

Gusty winds and the chance of thunderstorms into Tuesday will heighten the risk of renewed growth, the California Department of Forestry and Fire Protection said in a statement.